A wildfire that turned a historic Hawaiian town to ashes killed at least six people, officials said Wednesday, with desperate residents jumping into the ocean in a bid to escape the fast-moving flames.

US Coast Guard officers plucked at least a dozen people from the water as emergency services were overwhelmed by a disaster that appeared to have erupted almost without warning.

"I'm sad to report that just before coming on this, it was confirmed we've had six fatalities," Maui County Mayor Richard Bissen told a press conference.

"We are still in a search and rescue mode and so I don't know what will happen to that number."

At least 12 people have been treated in hospital for serious injuries, with two in critical condition. A number of those hurt have been transferred to other facilities for specialist care, the Maui Now website reported.

More than 270 buildings have been damaged or destroyed in the seriously affected town of Lahaina, officials said.

"Much of Lahaina on Maui has been destroyed and hundreds of local families have been displaced," said Governor Josh Green of the 12,000-resident historic town, which is popular with tourists.

Video posted on social media showed blazes tearing through the heart of the beachfront town and sending up huge plumes of black smoke.

"People are jumping into the water to avoid the fire," US Army Major General Kenneth Hara, the state adjutant general, told Hawaii News Now.

The Coast Guard said it had "successfully rescued 12 individuals from the waters off Lahaina" and it was sending other vessels to Maui.

Lahaina resident Claire Kent said she had seen her neighborhood razed less than an hour after she fled.

"The flames had moved all the way down to the end of the neighborhood," she told CNN.

"We were pulling out... onto the highway, you look back and there's cars with flames on both sides of the road, people stuck in traffic trying to get out," Kent said, describing the dangerous scene as "something out of a horror movie.

"I know for a fact people didn't get out," she said, adding that homeless people and those without access to vehicles seemed to have been trapped.

A first responder who was in the town after the blaze swept through described a scene of devastation.

"As you drive down the road... either way you look, it's honestly just rubble," the person told AFP on condition of anonymity because they were not authorized to speak to the press.

"It's ash and smoke and buildings just toppled over. Other than a random building here and there, everything's just rubble on the ground."

The individual said the death toll would almost certainly rise once the area could be searched properly.

"With how much charred materials there were... I don't think much is alive in there," they said.

"There were probably a lot of people who were caught off guard. It was pretty all-consuming."

- Water on fire -

Claire Kent, the Lahaina resident, described how power and cell phone coverage had been knocked out Tuesday, and she had been unaware of any approaching danger until a sudden shift of wind sparked panic.

"It was all just word of mouth, like people running down the street saying 'you need to get out.'

"There were guys riding around on bicycles, just screaming at people to leave."

For those who managed to flee, there was worry over missing family.

"I still don't know where my little brother is," Tiare Lawrence told Hawaii News Now. "I don't know where my stepdad is."

Chrissy Lovitt told the outlet every boat in Lahaina Harbor had burned.

"It looks like something out of a movie, a war movie," Lovitt said. "The water was on fire from the fuel in the water."

- Winds up to 80 mph -

Sylvia Luke, the state's lieutenant governor, said the fires were caused by dry conditions and fanned by powerful winds from Hurricane Dora, which is churning hundreds of miles south of the islands, but not expected to make landfall.

She said the fires have burned hundreds of acres and were being fanned by winds up to 80 miles (130 kilometers) per hour.

Almost 13,000 people were without power on Maui, according to tracking website PowerOutage.us.

Maui county officials said more than 2,100 people were in shelters, and a further 2,000 travelers were stranded at the airport.

President Joe Biden said he was mobilizing all resources to help.

"I have ordered all available Federal assets on the Islands to help with response," Biden said.

"The Hawaiian National Guard has mobilized Chinook Helicopters to help with fire suppression and search and rescue on the Island of Maui.

"The US Coast Guard and Navy Third Fleets are supporting response and rescue efforts."