About 500 residents were evacuated from their homes following a fire in a Braddon apartment block early this morning.

Just after 5am ACT Fire and Rescue responded to reports of a fire alarm on Ainslie Avenue.

Upon arrival firefighters located a caravan on fire in the basement of a multi-storey apartment block.

Residents were evacuated as firefighters worked to contain the fire that spread toxic smoke throughout the complex.

5 Pumpers, 3 Commanders, Breathing Apparatus Support, Hazmat, and other support trucks responded to the scene.

Several residents are still unable to return to the apartments due to hazardous gases inside the building.

Ainslie Avenue remained closed Eastbound for several hours.

ACT Policing and ACT Ambulance Service were also in attendance.

There were no reports of injuries.