Hawaii suffers worst flooding in more than 20 years as heavy rains sweep island

They warned that more rain was expected during the weekend.

Muddy floodwaters smothered vast stretches of Oahu's North Shore, a community world-renowned for its big-wave surfing.

Raging waters lifted homes and cars and prompted evacuation orders for 5,500 people north of Honolulu. Authorities cautioned that a 120-year-old dam could fail.

Governor Josh Green said the cost of the storm could top one billion dollars, including damage to airports, schools, roads, people's homes and a Maui hospital in Kula.

"This is going to have a very serious consequence for us as a state," Mr Green said at a news conference.

Most of the state was under a flood watch, with Haleiwa and Waialua in northern Oahu under a flash flood warning, according to the National Weather Service.

Mr Green said his chief of staff spoke to the White House and received assurances the islands would have federal support.

No deaths were reported and no-one was unaccounted for.

About 10 people were taken to hospital with hypothermia, the governor said.

Crews searched by air and by water for people who had been stranded - efforts that were hampered by people flying personal drones to get images of the flooding, said Ian Scheuring, a spokesperson for Honolulu.

The National Guard and Honolulu Fire Department airlifted 72 children and adults who had been attending a spring break youth camp at a retreat on Oahu's west coast called Our Lady of Kea'au, according to city and camp officials.

The camp is on high ground but authorities did not want to leave them there, Mr Green said.

The mayor said the flooding was the state's most serious since 2004 floods in Manoa inundated homes and a University of Hawaii library.

Dozens - if not hundreds - of homes were damaged on Friday but officials have not been able to fully assess the destruction, Honolulu mayor Rick Blangiardi said.

Some 5,500 people were under evacuation orders.

"There's no question that the damage done thus far has been catastrophic," he said.

Officials blamed some of the devastation on the sheer amount of rain that fell in a short amount of time on saturated land.

Parts of Oahu received 8in to 12in (20cm to 30cm) of rain overnight.

Kaala, the island's highest peak, got nearly 16in (40cm) in the past day, the National Weather Service said.

More rain was expected: Mr Blangiardi said 6in to 8in (15cm to 20cm) of rain was forecast to fall on Oahu in the next two to three days.

Winter storm systems known as "Kona lows", which feature southerly or southwesterly winds that bring in moisture-laden air, were responsible for the deluges in the past two weeks.

The intensity and frequency of heavy rains in Hawaii have increased amid human-caused global warming, experts say.

Officials have been closely watching the Wahiawa dam, which has been vulnerable for decades, saying it was "at risk of imminent failure".

Water levels in the dam receded by late Friday but that could change if more rain falls.

Overnight into Friday, the dam went from 79ft to 84ft (24 to 25.6 metres) - just 6ft (1.8 metres) shy of what it can handle, authorities said.

As she prepared to evacuate to a friend's home on higher ground, Waialua resident Kathleen Pahinui told The Associated Press in a phone interview that the ageing dam is a concern every time it rains.

"Just pray for us," she said.

"We understand there's more rain coming."

The state has said Wahiawa dam has "high hazard potential", and that a failure "will result in probable loss of human life".

The earthen dam was built in 1906 to increase sugar production for the Waialua Agricultural Company, which eventually became a subsidiary of Dole Food Company.

It was reconstructed following a collapse in 1921.

The state has sent Dole four notices of deficiency about the dam since 2009 and five years ago fined the company 20,000 dollars for failing to address safety deficiencies on time, according to records.

Afterwards, Dole proposed to donate the dam, reservoir and ditch system to the state in exchange for the state's agreement to repair the spillway to meet and maintain dam safety standards.

The state passed legislation in 2023 authorising the dam's acquisition.

It also provided five million dollars to buy the spillway and 21 million dollars to repair and expand it to comply with dam safety requirements.

But the transfer has not been completed.

A state board is due to vote on the acquisition next week.

"The dam continues to operate as designed with no indications of damage," Dole said in an emailed statement.

The state regulates 132 dams across Hawaii, most of them built as part of irrigation systems for the sugar cane industry, according to a 2019 infrastructure report by the American Society of Civil Engineers.