SAN FRANCISCO, CA — Two firefighters were injured battling a third-alarm blaze Wednesday morning at a building in San Francisco that is underdoing construction, according to authorities.

The two firefighters were helping fight the blaze when they fell roughly 10 feet through a floor in the whole, according to the San Francisco Fire Department.

They have since been taken to a local hospital, where they are in stable condition, San Francisco Fire Department Chief Dean Crispen said.

The two firefighters didn’t suffer any smoke inhalation because they had their masks on, but they may have suffered back injuries, Crispin said, adding that they’re still currently being evaluated at the hospital.

Four people were also displaced as a result of the fire, authorities said.

3 – ALARM FIRE San Francisco Fire is on the scene of a 3-alarm structure fire in the 2500 block of chestnut Street. The fire is still being fought inside the structure. At this time, two firefighters have been injured. Please avoid the area of chestnut between baker and… pic.twitter.com/o7iVvnxu4F
— SAN FRANCISCO FIRE DEPARTMENT MEDIA (@SFFDPIO) October 15, 2025

The fire broke out around 4:15 a.m. in the 2500 block of Chesnut Avenue, according to the San Francisco Fire Department.

When crews arrived, they were met with heavy fire coming from the second floor of a home, fire officials said. By the time crews extinguished the fire on the second floor, it had spread to the third floor and a nearby building, according to officials.

Crispin said the building where the fire broke out was under construction, and that may have led to “rapid advancement” of the fire.

Although the fire extended “significantly” to a building on the left and a little bit to one on the right of where the fire originated, crews were able to stop them both, Crispin said.

“Our firefighters did a fantastic job, very aggressive firefighting,” Crispin said. “Building under construction can provide many challenges, with uncovered walls and active plumbing and electrical work being done.”

It’s unclear what started the fire. Arson investigators are currently at the scene investigating.

The blaze was contained as of 5:18 a.m. Crews as of 7 a.m. were still working on checking the buildings for hotspots, authorities said.