A fast-moving grass fire that on Wednesday burned 20 acres in the East Bay hills is being investigated as a possible arson that sparked on University of California, Berkeley property, officials said.

The blaze was first reported at about 1:05 p.m. Wednesday near Grizzly Peak Boulevard and South Park Drive. By 7 a.m. Thursday, flames were about 50 percent contained.

About 1:30 p.m. Wednesday, UC Berkeley police arrested a person who had allegedly fled the scene of a vehicle accident on Grizzly Peak Boulevard. But Oakland police, who responded to the crash, were unable to determine whether the suspect is connected to the blaze, police said.

UC Berkeley officials described the fire as "a reckless wildland fire causing injury." One Cal Fire inmate firefighter suffered minor injuries after falling down steep terrain while battling the blaze, Oakland Fire Engineer Carleton Lightfoot said. No other injuries have been reported.

About half of the fire is within Oakland city limits and the other half is on land owned by the Lawrence Berkeley National Laboratory, fire officials said.

"We have a good handle on this incident," Lightfoot said at a briefing Thursday morning.

Lightfoot said fire crews expect "additional challenges" as the temperature rises again over the course of the day but are keeping the blaze from increasing in size despite a couple flare-ups overnight.

Grizzly Peak Boulevard would remain closed between Centennial and South Park drives until at least 8 p.m. Thursday, he said.

Fire department officials are advising people to avoid the area to allow crews to access the area of the fire without any trouble.

About 150 to 200 firefighters from nine fire agencies have battled the blaze.

A five-alarm brush fire burned in the Oakland Hills on Wednesday, prompting a power outage and evacuations at UC Berkeley, officials said.

Editors note: An Oakland fire dispatcher said in an earlier version of this story that the fire was extinguished, but a fire engineer has since clarified that the fire is 50 percent contained.