An overnight fire has extensively damaged a six-storey apartment building in Dartmouth, forcing at least 63 people out of their homes.

Nobody is injured. Firefighters were called to the scene at 249 Windmill Rd. around 12:50 a.m. The fire started on a balcony on the sixth floor and spread to the roof.

Tenant Deirdre Hale says she woke up when she heard a bump above the unit she shares with her fiance, Nathan Stone. 

"I heard yelling outside and someone slammed into the glass door or our patio yelling, 'Fire,'" she said.

The Canadian Red Cross says the fire was contained to a handful of apartments, balconies and the roof. There is also smoke and water damage and the power was shut off, which means all tenants were evacuated.

A Red Cross spokesman said a reception centre was set up nearby, but by 6 a.m. most tenants had found family or friends to stay with.

The cause of the fire is still being investigated. Firefighters have escorted some people back inside the building to retrieve clothes and other essential items.