A helicopter drops flame retardant on trees on the northern end of the Lodge Complex Fire, near Leggett, California, on August 11, 2014. Picture: Christopher Chung, The Press Democrat

San Francisco -

Three trapped firefighters had to deploy their personal fire shelters as a rapid wind shift sent a Northern California wildfire burning over their location on Monday, authorities said. All three survived with no serious injuries.

The firefighters had created a predetermined safety zone earlier in the day and retreated there when the fire worsened at about 5.30pm on Monday, Beaver Fire spokesman Corey Wilford said. Still, the flames burned over their location. A thunderstorm produced winds as strong as 56km/h, causing extreme fire behaviour.

Wilford said all firefighters in the area were withdrawing as the thunderstorm approached. All personnel were safe late on Monday night, he said.

The three were not immediately identified. Wilford said he didn't know if they suffered any minor injuries.

The fire in Siskiyou County near Klamath River, California, has burned across nearly 100 square kilometres and was reported 30 percent contained.

The sheriff's office issued more mandatory evacuation notices on Monday, but Wilford did not immediately know how many homes were affected.

The Beaver Fire and a second Northern California blaze reportedly were threatening nearly 750 rural homes.

Meanwhile, crews were anticipating the possibility of more lightning strikes while battling a lightning-sparked wildfire in Mendocino County about 320km south-west of the Klamath blazes. The fire near Laytonville had burned through nearly 40 square kilometres and was threatening nearly 60 structures. Mandatory evacuation orders remained in place. - Sapa-AP