(CNN) -- California Gov. Arnold Schwarzenegger on Wednesday declared a state of emergency in Southern California's Kern County, scene of a wildfire that has burned more than 6,000 acres.
About 1,500 firefighters had 50 percent of the fire contained Wednesday evening, a Kern County Fire Department spokesman said.
The fire has destroyed at least one home, threatens many more and prompted evacuations, the office said.
The declaration orders "that all agencies of the state government utilize and employ state personnel, equipment and facilities for the performance of any and all activities" as coordinated by emergency management officials.
By Wednesday, some 6,136 acres had burned, U.S. Forest Service spokesman Lee Bentley said.
About 250 structures are threatened, including homes and 100 outbuildings, he said.
Four injuries, all minor, have been reported. Smoke is affecting elderly residents, Kern County fire spokesman Sean Collins said.
The exact number of people who have evacuated was not immediately known, but Bentley said that 27 people spent Tuesday night on cots and 12 others stayed in various RVs at a shelter site. Two others were at a second shelter, he said.
Kern County officials were trying to estimate how many people have left their homes.
"We did a reverse 911 call to the area affected. I'm waiting to hear back how many residences that went out to," Kern County spokesman Sean Collins said. "That's not to say that's how many people were evacuated, but it will give us an idea."
The fire broke out Sunday west of Bodfish. Authorities are investigating the cause. Arson is suspected, Bentley said.
CNN's Nick Valencia contributed to this article