Flames raced across treetops and through drought-stricken vegetation as firefighters scrambled Wednesday to keep a growing California wildfire from reaching a holiday resort city at the southern tip of Lake Tahoe after evacuation orders were expanded to neighbouring Nevada, according to an AP report.

Thick smoke from the Caldor Fire enveloped the city of South Lake Tahoe, which was all but deserted during a summer week usually bustling with tourists.

The National Weather Service warned that critical weather conditions through Wednesday could include extremely low humidity, dry fuel and winds gusting up to 30 mph (48 kph).

“With those winds, as it ran through the forest it created what’s called an active crown fire run, where the fire actually goes from treetop to treetop,” AP cited Stephen Vollmer, a fire behaviour analyst for the California Department of Forestry and Fire Protection, as saying.

He said embers were being cast up to a mile out in front of the fire, creating new ignition points, including in some parts of the dense forest that haven’t burned since 1940 or before.

The blaze was 3 miles outside of South Lake Tahoe by Tuesday afternoon, Cal Fire Battalion Chief Henry Herrera told KGO-TV.

Pushed by strong winds, the Caldor Fire crossed two major highways and swept down slopes into the Tahoe Basin, where firefighters working in steep terrain were protecting remote cabins.

Cal Fire Division Chief Erich Schwab said some homes burned, but it was too early to know how many.

Thick smoke prevented air firefighting operations periodically last week. But since then, nearly two dozen helicopters and three air tankers dumped thousands of gallons of water and retardant on the fire, fire spokesman Dominic Polito said.