A fire in a large apartment building in the Chinatown neighborhood early Friday morning left six people injured, including two firefighters, and temporarily displaced dozens of families.

At 3:43 a.m. Friday, the Los Angeles Fire Department responded to a fire that started at a construction site on Bunker Hill Avenue, then jumped to a nearby three-story apartment building, according to a news alert.

More than 130 firefighters went to the scene, extinguishing the fire in an hour and a half. What ignited the fire is still under investigation.

An estimated 70 people have been displaced from the apartment building while the Los Angeles Department of Building and Safety evaluates the residence to determine which units are safe to reoccupy.

Six people were injured by the fire, including a 90-year-old man who was transported to a nearby hospital in critical condition. A woman, 55, was taken to a hospital with a non-life-threatening burn injury. Two others were assessed for injuries but declined transportation to the hospital.

One firefighter was taken to an occupational health facility for an injury, and another was being treated on scene for possible heat exhaustion.

One area resident told KTLA 5 that the construction site where the fire began had become a homeless encampment, and neighbors had expressed concern that something like this could happen.

Fire officials have not said whether there were signs of an encampment.

Authorities said the incident might snarl traffic in the downtown area by West College, Alpine and Yale streets. Drivers are asked to take alternate routes.