Firefighters battling out-of-control blazes struggled with supplies in the ritzy Pacific Palisades area of the city, utility managers said, blaming an unprecedented challenge to the city's reserves.

Massive tanks supplying water to the area ran dry overnight as dozens of hoses were attached in an almost fruitless effort to save homes in a blaze that has leveled around 1,000 buildings.

"We have three large water tanks, about a million gallons each," Los Angeles Department of Water and Power chief executive Janisse Quinones told reporters.

"We ran out of water in the first tank about 4:45pm yesterday, we ran out of water on the second tank about 8:30pm and the third tank about 3am this morning.

"That's where the hydrants went dry."

Quinones said more water was being pumped to the area to help keep the hydrants flowing, but the size of the supply lines and the fact that water had to be pumped uphill was complicating matters.

"I need our customers to really conserve water, not just in the Palisades area, but the whole system, because the fire department needs the water to fight the fires," Quinones said.

"We're fighting a wildfire with urban water systems, and that is really challenging."

Quinones said residents in certain areas should boil their tap water because of low supplies and pollution.

"Because we're pushing the water system so hard, our water quality is decreasing. So we're going to be issuing a boil water notice this morning, and that will extend for about 48 hours," she said.

"The water quality is low. We have a lot of ash in the system, and so please, if you're going to be drinking water, you need to boil the water."

Four major fires were burning around Los Angeles. Two people are known to have died, with a large number of people badly hurt, officials said.

Tens of thousands of people have been ordered to evacuate their homes, and firefighters are stretched extremely thin fighting blazes that remain entirely uncontrolled.