SAN FRANCISCO — A raging wildfire in rural Northern California that spread over 5 square miles and forced the evacuation of 200 homes in Napa County expanded Wednesday, officials said.

The Butts Fire in remote Pope Valley grew to 3,800 acres, said Daniel Berlant, a spokesman for the California Department of Forestry and Fire Protection.

It had damaged two homes and seven other structures and threatened hundreds more, officials said, but did not yet pose a threat to the major vineyards that are the area’s main business and claim to fame.

“It has not come anywhere close to what we consider Napa Valley wineries,” said Cate Conniff, a spokeswoman for the Napa Valley Vintners, a nonprofit trade association. “It is moving in the opposite direction, and it continues to move that way. We’re keeping an eye out on it.”

More than 1,000 firefighters were hoping to get a better handle on the blaze after they made progress overnight Tuesday, Berlant said. But fire activity increased about noon Wednesday as temperatures again soared into the 90s and the blaze continued burning northeast into neighboring Lake County. The blaze is 30 percent contained, officials said.

“We’re hoping that once the sun goes down, the temperature will as well and the humidity will also rise to give us another chance to increase containment,” Berlant said.

Crews have requested more bulldozers from across the state to assist the dozen on site in strengthening containment lines, Berlant said.

No injuries have been reported, and the cause of the fire remains unknown.

The fast-moving blaze began Tuesday afternoon in Napa County. Within hours, it covered 600 acres and then spiked to 2,700 acres by late evening as it spread northeast. State firefighters and crews from Napa, Lake and Solano counties spent a second day working in 90-degree weather on Wednesday.