A picture from the collapsed barricade scene was posted on Twitter. (Twitter)

Nineteen people were injured and nine sent to hospital after a barricade collapsed at a free Olympic rock concert in downtown Vancouver on Tuesday night.

The barricade gave way when the crowd of more than 7,000 partygoers surged forward just after the Canadian band Alexisonfire began playing at the outdoor venue set up in the trendy Yaletown neighbourhood.

Four doctors and nurses at the concert site assessed 19 injured concertgoers and sent nine to hospital, Penny Ballem, manager for the City of Vancouver, told CBC News on Tuesday night after the accident.

On Wednesday afternoon, Ballem confirmed two people sustained lower leg fractures, while one person reportedly had an injured knee. Everyone else was assessed, treated and released with minor injuries on Tuesday night.

"No serious injuries, no head injuries, no crushed hands or anything like that, so we feel very, very gratified," she said.

"We had an audience full of young people. There was a surge against the front barrier and the front barrier gave way, and so people fell over," said Ballem.

Witnesses told CBC News that as people crowded toward the stage, they broke through a metal barrier.

"People were pushing and shoving. I was like at the front and the gates broke and snapped in half and went over the edge. Eventually there were 2,000 people pushing on me. I was on top of about eight people in about two seconds," said one concertgoer.

Show cancelled immediately

Officials immediately cancelled the rest of the show and promised to investigate what went wrong.

"Why the barrier gave way is still not clear, that will be completely deconstructed, we've had certified professionals, fire, police, everybody's assessed the site," said Ballem on Tuesday evening.

By noon Wednesday, Live Nation, which is producing the concerts, had replaced the entire barricade and the venue was reopened to the public, according to a statement released by the city. Neither the city nor Live Nation revealed why they believe the barricade failed.

Alexisonfire, of St. Catharine's, Ont., is one of a number of Canadian bands invited to play as part of LiveCity Vancouver, a federally funded initiative to provide what organizers call "free, fun and family Games-time memories."

The Yaletown LiveCity venue includes a number of tents erected by corporate sponsors, as well as a large open-air section where people can watch live concerts or televised Olympic events.