California wildfires grow as strong winds fan flames

Fire crews are clearing brush and setting sprinklers to protect two groves of giant sequoias as a massive week-old wildfire rages along the remote northwest edge of Yosemite National Park. (Jae C. Hong/Associated Press)

A wildfire burning on the northern border of Yosemite National Park grew more than 18 square kilometres overnight as firefighters have gained little ground in slowing it.

On Sunday morning the 536-square-kilometre inferno was just seven per cent contained.

Fire officials say crews are focused east of the North Fork of the Tuolumne River, and are struggling to keep the fire from encroaching more into the park.

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Firefighters were bracing for strong south winds of up to 41 kph, so officials say the fire is likely to continuing growing.

Yosemite crews are cleaning brush and setting sprinklers in an effort to protect two groves of giant sequoias that are threatened by the fire.

The fire is one of the biggest in California history. Investigators are trying to determine how it started.