US July 4 revellers who were stranded by a wildfire in a mountainous California region have been safely evacuated.

However, fire continues to burn through through forests in Sierra Nevada Gold Country – a top tourist destination – on Tuesday, officials said.

The blaze that broke out on Monday afternoon tripled in size overnight to more than 4.7 square miles by Tuesday morning.

The Electra Fire affected a recreation area that was packed with people, forcing 85 to 100 celebrating the holiday at a river to take shelter at Pacific Gas & Electric Co facility, said Amador County Sheriff Gary Redman.

All were later safely evacuated, Mr Redman told The San Francisco Chronicle late on Monday night.

Evacuations were ordered in Amador and Calaveras counties.

Mr Redman said the cause of the fire was not known, but that it started in the Vox Beach area of the North Fork Mokelumne River.

He said that could suggest fireworks or a barbecue as a potential cause.

Vox Beach is about 55 miles east of Sacramento.

Several other small fires were burning in the state.