(CNN) — Evacuations have been ordered with a dam on Hawaii’s Oahu island at risk of imminent failure as the second significant storm in a week pounds the state.

Catastrophic flash flooding from the storm has already destroyed homes, forced rescues and cut off towns in northern Oahu.

The Wahiawa Dam “may collapse or breach at any time,” according to an alert from the Oahu Department of Emergency Management. Residents in the towns of Waialua and Haleiwa have been told to leave immediately due to “potential life-threatening flooding” and a flash flood warning has been issued for the area until 1:15 p.m HST.

“Do not stop to pack or prepare your home. Only take items ready to go,” the alert said.

The North Shore has been under flash flood warnings since early Friday as heavy rain lashes the island. It’s unclear how many homes have been destroyed in the area, Oahu Department of Emergency Management spokesperson Molly Pierce told CNN earlier Friday.

Emergency crews have rescued some people “directly from rooftops,” Hawaii Gov. Josh Green told CNN affiliate Hawaii News Now.

“There was a group of 70 people who were surrounded by water up at a camp site up on the North Shore,” Green said. “I was told they are safe right now, but they were having difficulty getting out because there was so much water around them.”

The Hawaii National Guard has also been activated, Green said in a social media post Friday. “Additional resources are continuing to deploy across Oʻahu. We are coordinating closely with state and county partners to support evacuations, open shelters, and keep our communities safe.”

Emergency responders struggled to access the flooded area early Friday morning, with two main roadways into it — Kamehameha Highway and Kaukonahua Road — flooded, emergency management spokesperson Pierce said.

“All points into the area are currently flooded, both coming in from central Oahu and from the Kahuku North Shore side. All routes in are flooded right now,” Pierce added.

A flash flood emergency — the highest-level flood warning — was issued for the area until 11 a.m. HST, or 5 p.m. ET.

“This is a FLASH FLOOD EMERGENCY for Northern Oahu. This is a PARTICULARLY DANGEROUS SITUATION. SEEK HIGHER GROUND NOW!” the warning from the National Weather Service said.

“This is an ultra-rare flooding event,” said National Weather Service Honolulu Meteorologist Robert Bohlin.

The last flash flood emergency issued by the weather service in Honolulu was more than five years ago, in March 2021.

Heavy bands of rain from a new Kona storm have soaked Oahu overnight, dumping two-to-three months’ worth of rain in the last 24 hours. Rainfall totals have reached 6 to 12 inches on the northern half of the island.

The ground is saturated from last weekend’s major storm, so water is running off quickly and causing more serious flooding.

Dams and reservoirs on the island are also at extremely high levels, but are starting to come down with a lull in the rain, though officials are monitoring them given the already high saturation from the earlier storm.

More heavy rain is possibly on Oahu and the rest of the islands through this weekend, and a flash flood watch is in effect until Sunday afternoon.

Heavy rain and strong winds from last weekend’s storm set off dangerous flooding, landslides, sinkholes and knocked out power to thousands across the state.

The storm dumped more than 15 inches of rain across all of Hawaii’s islands, but Maui’s higher elevations received the most, recording more than 2 feet.

Maui also saw some of the worst impacts: Flooding destroyed at least one home and a condo building, according to CNN affiliate Hawaii News Now. Emergency crews also conducted flood rescues in South Maui and widespread road closures left some residents stranded, Hawaii News Now reported.

Gov. Green issued several emergency proclamations due to the storm and a disaster relief period is in effect through April 13.

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