A SOLICITOR shot dead by a gunman at a busy Melbourne city intersection may have been just a good samaritan helping a woman involved in a domestic dispute, police and witnesses say.
The gunman was on the run this morning after shooting three people on the corner of Flinders Lane and William Street, killing the man and wounding a woman and a man.
The man killed was a 43-year-old solicitor, police said today.
The solicitor was blasted in the chest at point blank range and died at the scene an hour later, despite the efforts of paramedics to revive him.
Paramedics fought for an hour to save the man before he died. Read story here
Police said this afternoon they had identified a person of interest, who was believed to be the gunman, but refused to release further details for fear of jeopardising their investigation.
The gunman fled on foot after the 8.15am shooting and police later found a handgun at a nearby construction site, which was believed to be that used in the incident.
As heavily-armed police searched for the shooter, aged in his late 20s or early 30s, office workers were told to stay put and not panic.
Witnesses and police said the gunman appeared to be involved in a violent domestic dispute with a woman in a taxi and when two men intervened, he shot all three down.
Police appealed for the taxi driver to come forward.
Police said the shooting followed an earlier incident outside a King Street nightclub.
Heavily armed police are searching the centre of Melbourne for the gunman who opened fire at a city road intersection before fleeing on foot.
Police said a handgun had been found a short time ago at a Melbourne city construction site near where the three people were shot.
The gun was found at a construction site on the corner of Flinders and Queens streets they said, but had yet to confirm if it was the one used in the shooting spree.
Inspector Glenn Weir said a witness had found the gun and reported it to police.
"I understand he's located the firearm and not the person.
"(It was) a handgun I can confirm and there are reports that it's a semi-automatic handgun but I can't confirm that."
One man died at the scene despite paramedics attempting to resuscitate him, while a man in his 30s and a 24-year-old woman were this morning in a critical condition, undergoing surgery at Royal Melbourne Hospital.
Eyewitnesses said the gunman shot the two men and one woman after struggling with the woman as she got out of a taxi.
Inspector Weir said police were speaking with a large number of witnesses at the shooting scene.
He said it appeared the shooting was a domestic incident between the shooter and the female taxi passenger and not a gang-related or random act.
"It does appear that there was a relationship between the female and the male suspect and certainly we're not looking that it's a random act, certainly not gang-related, it appears as though its a domestic related incident."
He said the two male victims appeared to be good samaritans who had stopped to come to the woman's aid as she struggled with the shooter in the street.
"That's certainly one of the avenues of inquiry that we're undertaking and that looks more likely as time goes on," Insp Weir said.
Malcolm Bates, a witness, said before the shooting broke out the gunman grabbed a woman by the neck as she sat in a taxi, and tried to get into the vehicle.
"The lady got away and he turned and shot three people basically point blank," Mr Bates said. "I was right across the road."
Eyewitness Zali said the gunman was "as cool as a cucumber" as he cold-bloodedly blasted his victims.
"He just went bang, bang, bang, there was no mucking around," she told ABC Radio.
"There were five shots fired and the people went straight down to the ground. There wasn't even a scream, just a whimper."
Zali said the drama began while she was on her way into work.
"I heard what sounded like a cap gun and I turned my head over to look to the right of me and saw the gentleman shoot the three people and them go down.
"I quickly pulled over to the side of the road and ran across the road and he'd taken off up the road (and) ran up towards Flinders Street station.
"It's amazing what happens in a time of crisis because the people that flocked around to help those that had been hurt were just excellent, in the sense of as much as there were some screams of hysteria, the sense of protectiveness and getting help and the number of people (calling for help) on the phone was just outstanding."
Bystander Ross Murchie said he saw the gunman grabbing a woman by the neck and hair.
"She was screaming and a guy had her by the hair," Mr Murchie told ABC Radio.
"She tried to grab hold of a taxi that was going by and the couple of bystanders went over to ask what was happening.
"He let go of her hair, pulled out a gun and shot them all."
The area around the shooting was locked down as police searched for the gunman, with offices sealed off and people kept away from nearby workplaces as the drama unfolded.
Carly, who was in the Rialto building on Collins Street, said people in her building had been told not to move.
"We've just been told that none of our people who are waiting downstairs to come upstairs can come up," Carly told 3AW.
"They've blocked off all the access to the floors in our building because they're still looking for the shooter.
"We're not allowed to go anywhere and no-one is allowed to come up into the building."
One worker, Joanne, said she left her building for cigarettes at 8.15am, and heard gunshots.
"I saw police cars coming from everywhere," she told AAP.
"I thought 'wow'. What is happening?"
She said she was worried someone she knew may have been shot.
"You hope it's not them, but you just don't know."
The gunman was last seen heading east after the shooting on the corner of Flinders Lane and William Street at 8.15am (AEST).
< p>Police Inspector Glenn Weir said police had cordoned off an area around the shooting scene near the corner of Flinders Lane and William Street and were combing the district to find the man.
Inspector Weir said it appeared the gunman knew the victims.
"There is no suggestion this is a random act - it appears there was a relation with the gunman and the victims, so we are asking people not to panic," he told ABC radio.
Malcolm Bates, a witness, said before the shooting broke out the gunman grabbed a woman by the neck as she sat in a taxi, and tried to get into the vehicle.
"The lady got away and he turned and shot three people basically point blank," Mr Bates said. "I was right across the road."
He told ABC radio the gunman then ran down Flinders Lane toward the city centre.
He said the whole scenario took no longer than "the wink of an eye".
Police wearing bullet-proof vests were scouring the area, and police helicopters hovered overhead.
Insp Weir said the last confirmed sighting of the gunman was east of the shooting scene, on Flinders Lane.
Police and ambulance paramedics were called to Fitzroy Lane shortly after 8.15am, where they found one person in a critical condition and two others wounded.
Police have since confirmed one person has died and two have been taken to Royal Melbourne Hospital.
Witnesses heard a volley of gunshots before the victims were discovered.
The gunshot wounds are believed to be to the victims' upper bodies.
Cherie Harding, a worker in the Rialto building opposite the shooting scene, said several of her colleagues heard up to four shots.
Ms Harding said she saw ambulances at the scene and stretchers being used to transport patients.
"There are a few people here who heard them (gunshots),'' she said.
Inspector Weir asked people in the area not to panic.
"There is an extensive search underway to try and find the offender at the moment,'' Insp Weir said.
"There are numerous police attending to the search within the vicinity of the incident and there is a large cordon and containment operation underway as we speak.
"We are just asking the public not to panic and assist police if requested and if you have no business being in the vicinity of Flinders Lane and William Street please keep out of the area.''
The gunman is described as wearing black jeans and a denim jacket, with short light brown hair.
The Victoria Police homicide squad this morning took over the investigation as the police Special Operations Group joined the search for the gunman.
Police have blocked off a number of city streets until further notice and have also begun evacuating some buildings.
Police in Melbourne, Australia are on the hunt for a gunman who killed a man and injured two others in the city's central business district this morning. 

Officials warned all office workers to remain indoors, and train services to Flinders Street Station were temporarily on hold, as investigations were carried out on the intersection of Flinders Lane and William Street.

Malcom Bates, who witnessed the shootings at around 8:15 a.m., said the gunman grabbed a woman from inside a taxi. "The lady got away and he turned and shot three people basically point blank," Mr Bates said. "I was right across the road". He said that the incident took no longer than the "wink of an eye".

Paramedics struggled to revive the one victim for almost an hour before declaring him dead at the scene. The two injured people have been taken to the Royal Melbourne Hospital in a critical condition.

Police believe the incident began at the Bar Code 24-hour bar in King Street, when a woman attempted to get into a taxi. She was apparently grabbed by the hair by the gunman who then shot her and two men who attempted to come to her aid.

Police have identified the gunman as Christopher Wayne Hudson, aged 29. They believe him to be a member of the Hells Angels bikie gang. Police have described Hudson as about 180 cm tall, with short brown hair and wearing a dark tracksuit top and dark denim jeans.

A building worker on a construction site on the corner of Queen and Flinders Streets has reportedly discovered a handgun. It is understood the gunman may have thrown the weapon into the site as he fled the scene.