Lying in the street and seemingly locked in a kiss as chaos erupts around them, a young couple appear oblivious to the charging crowds and baton-wielding riot police.

The photograph, taken amid Vancouver's hockey riots, has been tweeted around the world. But the photographer who took it is still not sure what the picture really shows.

Canada-based photojournalist Richard Lam took the photograph while covering the riots that followed the Vancouver Canucks' 4-0 loss to the Boston Bruins in the Stanley Cup.

The photographer was being buffeted by rioters and riot police when he spotted the couple. "I was about 20 or 30 yards away," he said. "There were these two people on the ground in this empty street. Initially I thought one of them was hurt." He took a few shots and then the moment was lost.

"It was complete chaos. Rioters set two cars on fire and then I saw looters break the window at a neighbouring department store," he said.

"At that point, the riot police charged right towards us. After I stopped running, I noticed in the space behind the line of police that two people were lying in the street with the riot police and a raging fire just beyond them.

"I knew I had captured a 'moment' when I snapped the still forms against the backdrop of such chaos but it wasn't until later when I returned to the rink to file my photos that my editor pointed out that the two people were not hurt, but kissing."

"Everyone has been asking who they are," said Lam but he has no idea and never had the opportunity to speak to them.

Even now he's not sure whether the picture shows a couple kissing or whether one of the two people is hurt. "I keep looking at the picture but I don't know what I think any more," he said.

[This update was inserted on 17 June 2011: After publication of this Guardian article, further details about the couple and the incident emerged. A subsequent Guardian online piece is headlined Vancouver kiss couple 'were knocked down by riot police'.]

Officials in Vancouver said almost 150 people required hospital treatment and almost 100 were arrested during the riot.

A spokeswoman for the local health authority said three stabbing victims had been admitted and an one man was in critical condition with head injuries after a fall from a viaduct.

Rioting and looting left cars burned, stores in shambles and windows shattered over a roughly 10-block radius of the city's main shopping district.

Police Chief Jim Chu said nine officers were injured, including one who required 14 stitches after being hit with a thrown brick. Chu said some officers suffered bite marks. He said 15 cars were burned, including two police cars.

He called those who incited the riot "criminals and anarchists" and said officers identified some in the crowd as the same people who smashed windows and caused trouble through the same streets the day after the 2010 Winter Olympics opened in 2010.

"These were people who came equipped with masks, goggles and gasoline," he said. "They had a plan."

Chu said those who stood by and filmed and cheered also bear some responsibility.

Assistant Fire Chief Wade Pierlot said people had to be rescued from rooftops and bathrooms where they had hidden for safety. He said some people moved burning dumpsters away from buildings to prevent further damage.

• This article was amended on 17 June 2011 to insert an update.