Authorities Tuesday morning were on the scene trying to determine what sparked a fire that heavily damaged a Burnsville apartment building.

Firefighters and police were able to walk residents in 36 units through thick smoke and out of the Pines of Burnsville safely. No one was hurt, said Burnsville Fire Chief BJ Jungmann.

Crews were called to the complex on the 1000 block of W. Burnsville Parkway just after 1 a.m. The fire grew to four alarms and several neighboring agencies helped extinguish the blaze, Jungmann said.

Alarms were sounding when police and firefighters arrived, but the building did not have a sprinkler system. It did meet code as it was built before such systems were required, he said.

The fire was believed to have started on the third floor on the courtyard side of the building. The building sustained major damage, including part of the roof falling in. It was not immediately clear when residents would be able to return, Jungmann said.

The Red Cross and the Salvation Army were providing assistance to displaced residents.