The Pacific Gas & Electric company said it would 'take accountability' if found responsible for the explosion [AFP]

An evening gas-line explosion in a neighbourhood south of San Francisco has set fire to hundreds of homes, leaving at least four people dead and dozens injured.

Firefighters battled the wind-fed flames on Thursday night as they spread across a swath of San Bruno, a suburb just south of San Francisco and west of the busy San Francisco International Airport.

The fire began when a "gas transmission line" running underneath the neighbourhood ruptured at around 6pm, according to a statement released by the Pacific Gas & Electric company (PG&E), which provides power to the majority of California residents and owns the line.

The main fire, fed by the gas line, raged into the night before fading. Authorities cut power to the neighbourhood as emergency crews worked to extinguish the secondary fires.

PG&E said it would "take accountability" if it is determined that the company is responsible for the ruptured line.

The company earned total revenues of around $14.6bn in 2008 and has been involved in numerous environmental and safety controversies in California, most notably the case of groundwater contamination near the town of Hinkley, which led to a legal case dramatised in the film Erin Brockovich.

'Hair-burning' heat

Twitter user 'wiggs,' whose parents live in the neighbourhood, posted images of the fire

"I heard a sound like a low flying plane, then all of a sudden the house shook," said Tina DiIoia, who was with her baby in their condominium in San Bruno when the explosion occurred less than a kilometre away.

"Then there was another explosion. I went outside and there was debris falling from the air."

Other witnesses reported large pieces of ash falling from the sky and said they thought the initial explosion was an earthquake - a common occurrence in California.

One witness, Joe Simpson, who lives around a kilometre from the explosion, told the San Francisco Chronicle newspaper that he saw flames from the gas line erupting 60 to 90 metres into the air.

Another man, Omar Naber, who lives with his mother just several hundred feet from the site of the explosion, told the Chronicle the two found that the inside handle of their front door was too hot to touch when they first tried to rush out of their home.

Once they got outside, the heat was so intense that it burned the hair off Naber's arm, he said.

Some residents told the media that the smell of gas has been in the air for days or possibly weeks.

Source: Agencies