Oahu’s emergency office has ordered residents in the Waialua area to ‘leave now’ amid risk of road failures.

Heavy rains have prompted widespread evacuations on the north shore of the island of Oahu, as the state of Hawaii experiences its worst flooding in 20 years.

Early Saturday morning, Oahu’s Department of Emergency Management issued dire warnings for residents in communities like Waialua, part of the United States.

“Residents in the Waialua area are strongly urged to LEAVE NOW,” one message overnight read. “The remaining access road out of Waialua is at high risk of failure if rainfall continues.”

Already, evacuation orders are in effect for nearly 5,500 people in the region north of the state capital, Honolulu.

No deaths have been reported so far, but at least 200 people have been rescued as muddy, brown floodwaters engulfed streets and neighbourhoods. Ten people have been hospitalised with hypothermia after being plucked from the storm waters.

A youth camp run by the organisation Our Lady of Kea’au was also evacuated, and 72 adults and children were airlifted from the site as a precaution, according to officials.

More rain is expected to bear down on the Hawaiian islands over the coming days.

Governor Josh Green estimated that the damage could exceed $1bn in costs, and he described the floodwaters in some areas as “chest-level”.

“We’ve evacuated the whole region now,” Green said in a video statement on Friday. He emphasised that the Hawaii National Guard was out in force to help with emergency efforts.

“I’ve mobilised even more military reserves, and we have the troops coming in from Schofield [a military base] to help. The coastguard will be out there to do search and rescue if, God forbid, any of our loved ones have been washed away with housing.”

Of particular concern is the 120-year-old Wahiawa dam, which officials warned was “at risk of imminent failure”.

A 2022 document from the Hawaii Department of Land and Natural Resources identified the Wahiawa structure as “a high hazard potential dam, as a failure of the dam will result in probable loss of human life”.

Built in 1906 and reconstructed following a collapse in 1921, the dam was designed to increase local sugar production.

It was eventually acquired by the Dole Food Company, which has received four notices since 2009 about the dam’s deficiencies.

In April 2021, the food giant was fined $20,000 for failing to safely maintain the dam and its spillway. Experts at the time warned the dam might not be able to safely handle flooding, though representatives for Dole refuted the assessment.

“The dam continues to operate as designed with no indications of damage,” Dole said in a statement to The Associated Press.

The state of Hawaii passed a law in 2023 to acquire the dam, but the transfer is not yet complete.

On Friday, water levels at the earthen dam rose from 24 to 25.6 metres (79 to 84 feet), just 1.8 metres (6 feet) below its capacity.

The rising waters ravaging the state are considered some of the worst since the 2004 floods in Manoa, a neighbourhood of Honolulu.

Honolulu Mayor Rick Blangiardi estimated that hundreds of homes have been affected by the floodwaters, but that the full scope of the damage has yet to be assessed. He added that Oahu is expected to receive an additional 15 to 20cm – 6 to 8 inches – of rain over the next few days.

“There’s no question that the damage done thus far has been catastrophic,” Blangiardi said.