GILBERT, Ariz. — Fire officials on Sunday were trying to determine what caused a major fire at a construction site in a Phoenix suburb that led to dozens of evacuations.

Mike Connor, a spokesman for the Gilbert Fire Department, said investigators were back at the scene Sunday morning after working through the night.

The blaze began Saturday at an apartment complex under construction and sparked fires at nearby houses.

Connor said more than 70 people were evacuated from a nearby apartment complex. The origin of the fire has not been determined.

A firefighter with burns on his hand and three police officers with smoke inhalation were treated at the scene. A second firefighter was hospitalized for a heat-related injury but is recovering.

American Red Cross spokeswoman Diana Rodriguez said 11 people are receiving shelter while other families had a place to go. The town’s Public Safety Complex amphitheater was open for evacuees, officials said.

More than 120 firefighters worked to contain the five-alarm fire, and a road was closed to traffic.

Fire officials said the unfinished wood of the building under construction burned faster, and most of the structure collapsed. The complex was made up of at least seven, three-story buildings.

The National Weather Service in Phoenix reported winds of about 17 miles per hour, with gusts up to 25 miles per hour, in the area of the fire. Smoke could be seen for miles away.

ASSOCIATED PRESS