iReporter Karl Loo lives near the building and was there about a half-hour after the fire started. See his dramatic video from the scene.
Beijing, China (CNN) -- Four suspects have been detained in a China high-rise fire that killed 53 people, state media said Tuesday.
Monday's fire has hospitalized at least 70 other people, including 17 who were seriously injured, officials said.
A preliminary investigation indicated that unqualified welders caused the fire, the Xinhua news agency said. The welders violated safety rules, Xinhua said.
The 28-story building was under renovation when it went up in flames.
Witnesses said a scaffolding caught fire, and flames then spread to the building.
"The fire became so big because the scaffolding contained a great amount of flammable materials," Zhu Zhixiang, a Shanghai firefighting official told state broadcaster CCTV. "Heavy wind at the time was another factor."
Firefighters rescued more than 100 residents from the burning building. The building houses 150 families, the news agency said.
"I can smell the smoke and police have pushed onlookers farther away," said Peijin Chen, a freelance photographer who lives across the street from the building. "I saw people taken out and put on stretchers."
CNN's Steven Jiang contributed to this report.
China's  said Tuesday that at least 53 people were killed in Shanghai during a deadly fire. The blaze, which occurred on Monday at 2:15 p.m.  (0615 ), consumed a 28-story high-rise apartment building in the city's .

The building was being renovated at the time of the fire, and was home to over 150 families. At least 100 victims have been admitted to area hospitals, although some later died. Most survivors were not seriously injured, but needed treatment for . Firefighters were still looking for survivors and over 70 were still hospitalized on the morning after the fire.

The fire was the worst in recent Shanghai history and took over 100 fire engines more than four hours to contain. Strong winds blew heavy smoke into the air, hampering rescue efforts by helicopters. The smoke was seen by witnesses around 15 kilometres (9.3 miles) away from the high-rise. The fire was largely extinguished by 6:30 p.m. local time (1000 UTC), allowing fire and rescue officials to enter the building.

The apartment building, built in the late 1990s, was home to mainly retired teachers. Some residents climbed down the scaffolding to escape, while others called for help but were unable to flee the blaze. "I saw at least four or five people hanging onto the scaffolding which covers the building, screaming for help," said Li Qubo, who was working near the high-rise.

The cause of the fire has not yet been determined, but local residents said fire safety regulations were not strict, and workers often tossed used cigarettes into the building's hallways. Qiu Jingshu, a 38-year-old worker who was outside the 18th floor when the fire struck, said he saw sparks from welding being done on an adjacent building fly over onto the high-rise. The sparks lit up foam on the scaffolding around the apartment, according to Qiu. "We had tried to put out the blaze, but the fire was so big and spread so quickly that we could barely escape ourselves," he said. Crews were said to have been installing insulation at the time of the fire, and witnesses saw construction materials on fire before the building was overtaken by flames.

Two nearby buildings were evacuated, and their residents were temporarily sent to local hotels, and a school. , China's , said that an investigation would determine who was responsible for the fire, so they could be punished accordingly. Meng said that a team had been formed under  to look into the disaster.

A similar incident occurred in Beijing early last year. In February 2009, the illegal use of fireworks  that gutted a 34-story building under construction at the time.

Shanghai has a population of about 20 million, housed mainly in high-rise apartments. Many buildings in the city are under construction or being renovated.