DENVER -- A unit inside a southeast Denver apartment complex caught fire Wednesday afternoon, causing extensive damage and several injuries.

Three people were injured and two were transported to local hospitals, said Denver Fire spokesman Phil Champagne.

The fire started on the second floor, on the southwest side of the Britannia Heights apartment complex, he said. He believes that the fire started with an explosion, perhaps from an oxygen tank. Unit 212 has a home oxygen unit, he said.

Neighbors said they heard two loud bangs just before the fire started.

To escape from the fire, some of the residents jumped from balconies on the lower floors. Others were rescued from the roof of the five-story building and some hung out on their balconies, waiting for help.

The complex is at 1255 S. Bellaire St., near Colorado Boulevard and Louisiana Avenue.

The cause of the fire is under investigation.