As the people of LA tried to save their burning homes, fire hydrants ran dry. This is why.

Crews battling multiple wildfires raging across Los Angeles are up against a near-perfect storm: intense wind, low humidity and, most troubling for residents, inadequate supplies of water to contain the blazes.

Authorities said their municipal water systems were working effectively but they were designed for an urban environment, not for tackling wildfires.

On Wednesday, at least three major blazes burned in LA County communities simultaneously, including a fire in the affluent Pacific Palisades neighbourhood, an area west of downtown LA dotted with multimillion-dollar celebrity homes built along steep canyons.

Iconic Sunset Boulevard went up in an inferno. Image: Getty.

Jay Lund, a professor in civil and environmental engineering at the University of California Davis, said city water tanks are typically designed to be able to put out localized fires, not widespread fires like the ones blazing in Los Angeles.

"It's not a matter of there's not enough water in Southern California, it's a matter of there's not enough water in that particular area of Southern California just for those few hours that you need it to fight the fires," Lund said.

Watch Seven's coverage as the wildfire sweeps through Los Angeles. Story continues below.

Across the county, more than 70,000 people were ordered to evacuate and at least five were left dead as fierce winds fuelled the fires, which have burned unimpeded since Tuesday. The fires have destroyed hundreds of buildings.

"A firefight with multiple fire hydrants drawing water from the system for several hours is unsustainable," said Mark Pestrella, director of Los Angeles County Public Works.

Janisse Quinones, CEO and chief engineer of the Los Angeles Department of Water and Power, said the demand for water to fight fires at lower elevations was hampering the city's ability to refill water tanks at higher elevations.

The lack of water hampered efforts particularly in Pacific Palisades, an upscale coastal enclave where a wildfire has consumed nearly 4900 hectares.

Fire fighters are trying to put out blazes on multiple fronts. Image: Getty.

The Los Angeles Department of Water and Power said that in advance of the windstorm, it had filled all available water tanks in the city, including three 3.8-million-litre tanks in the Palisades area.

The area had exhausted the three water storage tanks by early Wednesday, Quinones said in a press briefing.

The department urged Angelenos to conserve water, and said it had deployed 18 water trucks of 2000 to 4000 gallons since Tuesday to help firefighters.

Lund said the nature of the fires was such that it was nearly impossible to arrange enough water in advance.

"If everything catches fire at once, there's not going to be enough water for everybody," he said.

"There's just no way that you could fit the pipes to work to move that much water across that area in a short period of time."

As well, the number of California homes and businesses without electricity ballooned to more than 400,000 on Wednesday.

Featured image: Getty.