Two explosions near the Boston Marathon finish line have killed at least two and injured 23 others.

A chaotic scene erupted in the area, as paramedics treated people at the scene. Competitors, race volunteers and spectators were diverted away from the race route.

“There are a lot of people down,” said one man, whose marathon bib No. 17528 identified him as Frank Deruyter of North Carolina.

Marathon crews carried one woman with a bloodied leg to a medical area set up for the race. A Boston police officer was also said to have sustained a leg injury.

The incident happened approximately three hours after the first marathon runners were said to have crossed the finish line, however thousands of participants were still running.

There was a loud explosion on the north side of Boylston Street, near the photo bridge that marks the finish line.

Footage captured at the scene showed smoke rising from the blasts. Aerial footage also showed blood on the pavement in the Back Bay shopping and tourist area.

"There are people who are really, really bloody," said Laura McLean, a runner from Toronto, who was in the medical tent being treated for dehydration when the blasts occurred. "They were pulling them into the medical tent."

Cheri Falgoust was waiting for her husband, a marathon runner, when she heard – and felt – a loud boom.

"I was expecting my husband any minute," she said. "I don't know what this building is ... it just blew. Just a big bomb, a loud boom, and then glass everywhere. Something hit my head. I don't know what it was. I just ducked."

Authorities in Boston could not immediately confirm the number or severity of injuries.

Runners who had finished the race were diverted down Commonwealth Avenue and into a family meeting area.

Canadians in Boston needing emergency assistance can reach the Consulate General at 617-247-5100. If you are concerned for a friend that ran the Boston Marathon today, you can see their last check-in here: http://raceday.baa.org/individual.html