(CNN) -- Heavy smoke from the Lockheed Fire in northern California had cleared enough by Friday that authorities could see it had spread substantially from the day before and had destroyed two buildings.
The northern California fire was burning 4,100 acres by Friday, officials said.
A California Department of Forestry and Fire source said smoke had prevented authorities from accurately assessing the amount of damage.
"Now that the smoke has cleared we can get a better view of it," he said.
Hundreds of firefighters had managed to contain about 5 percent of the northern California wildfire that grew from 2,800 acres on Thursday to 4,100 acres Friday.
No injuries have been reported, according to Cal Fire's Web site.
California Lt. Gov. John Garamendi declared a state of emergency for Santa Cruz County, where the fire is burning.
Garamendi is acting as the state's chief executive while Gov. Arnold Schwarzenegger is in Massachusetts attending the funeral of his mother-in-law, Eunice Kennedy Shriver.
The governor is scheduled to return to California late Friday and to tour the Santa Cruz fire zone on Saturday.
The fire is moving alongside the Santa Cruz Mountains in Santa Cruz County, near the Pacific Coast, about 60 miles south of San Francisco.
The cause of the blaze, which began Wednesday night, was being investigated, said Cal Fire spokeswoman Megan McFadden. On Thursday, thousands of residents fled ahead of the fire.
Spokesman Daniel Berlante said about 675 firefighters were battling the blaze with air and ground resources.
A mandatory evacuation order was issued for about 300 households in the Swanton area Thursday. Berlante said up to 2,400 residents had evacuated in the Swanton and Bonny Doon areas.
Helbard Alkhassadeh traveled down the state's scenic Highway 1 Thursday between Davenport and Santa Cruz and submitted images of the blaze to CNN's iReport.
"I got to the point where the main plume was going over my head, and it was sprinkling ashes on me," he said. "It's an ominous feeling when you have ashes raining on you. It looks like a nice sunny day, then you drive into it, and it becomes like a volcanic cloud."
Earlier, Alkhassadeh said, most of the residents in the town of Bonny Doon evacuated as a precaution. Watch the fire rage »
"It's not directly affecting them, but they want to be absolutely sure until the last minute," he said.
A shelter was set up at the Vintage Church in Santa Cruz, about 10 miles south of the fire area.
Scott Bates, another iReporter, lives in Bonny Doon and said "everybody's packing." He estimated the fire was about four miles from his home. iReport: Are you there?
A fire in the same area of Bonny Doon last year forced the evacuation of about 1,500 residents, officials said.
CNN's Nick Valencia and Jason Hanna contributed to this report.