An early morning fire spread quickly through the top level of a Redwood City, California, apartment building Thursday, injuring four people, a fire official said.
"People did hear the alarms. People started to evacuate the building, and we were greeted with a lot of people coming out the building, which is a good sign," Redwood City Fire Marshal Jim Palisi told CNN affiliate KGO-TV.
The six-alarm fire was "pretty extensive" on the top floor of the four-story building, which includes 73 apartments, he said.
One of the four injuries was considered serious, while one was moderate and two were minor, Palisi said.
The first calls reporting the fire were received at 5:15 a.m., he said.
About a dozen people who live in the building have not yet checked in with the community center to let officials know they are all right, Redwood City spokesman Sheri Costa-Batis said.
Redwood City is about 25 miles south of San Francisco.