At Least 27 People Have Been Killed in Laos Dam Collapse. Here’s What to Know

A hydropower project under construction in Laos failed Monday night, releasing a catastrophic torrent of water onto the rural villages below, sweeping away homes and people in a muddy tide.

Hundreds were initially reported missing and 27 deaths have been confirmed.

Prime Minister Thongloun Sisoulith called it possibly the worst disaster to strike Laos in decades.

Officially, nearly 7,000 people have been rendered homeless after flash flooding inundated a half dozen villages in southernmost Attapeu province near the borders with Cambodia and Vietnam. Survivors were left clinging to trees, or stranded on a handful of rooftops peaking above the floodline.

Rescue operations and an investigation into what exactly caused the breach at the billion dollar Xe-Pian Xe-Namnoy hydropower project are underway, but details remain murky with several conflicting reports.

Here’s what we know.

The death toll

Twenty-seven people have been killed, and 131 people have been added to an official missing persons list, according to Prime Minister Sisoulith.

A senior Laos government official, declining to be named, told Reuters that dozens are dead, and said that he feared the final toll would be much higher.

The rescue effort

When the dam failed, millions of tons of water cascaded downstream. Photos and videos posted by state media showed villagers, some just young children, perched on rooftops to escape the flood.

As of Thursday, Prime Minister Sisoulith said everyone who was was stranded by the rising water has been rescued.

The area has been declared a disaster zone, and provincial authorities have requested donations of emergency aid provisions, including food, drinking water, medicine, cash and clothing.

Emergency shelter is also urgently needed, according to the UN Office for the Coordination of Humanitarian Affairs. Schools have been repurposed to house evacuated families, but another 1,300 tents are required.

A warning, too late

Just hours before the disaster on Monday, the Laotian, Thai and South Korean consortium behind the project warned that one of its dams was dangerously unsafe and would send walls of water surging downstream if it collapsed, VOA reports.

An official from South Korea’s SK Engineering & Construction (SK E&C), one of the companies building the project, confirmed to TIME that fractures were observed on the dam before the disaster, and an evacuation of the 12 surrounded villages was recommended.

He added that it remains unclear what caused the dam to fail, which occurred after unusually heavy rain.

Management from SK E&C have gone to the site for an emergency consultation, according to the official.

The dam

The structure that collapsed is reportedly one of three “earth-filled” auxiliary dams supporting the $1.02 billion Xe-Pian Xe-Namnoy hydropower project, a system of dams, reservoirs and channels.

As with dozens of other hydropower projects that impoverished and riverine Laos has okayed in its bid to become the battery of Southeast Asia, this one relied on foreign developers, and intended on exporting most of the electricity generated.

The 410 MWXe-Pian Xe-Namnoy project was slated to come online this year, with a plan to sell 90% of the power generated to Thailand.

Downstream impact

As water released by the dam continued to surge downstream, flash flooding reached neighboring Cambodia on Wednesday.

Officials in Stung Treng Province, about 100 miles south of the Xe-Pian Xe-Namnoy project, said 25,000 Cambodians along the Sekong River required evacuation to higher ground. About half the affected families were relocated as of Wednesday night, the government reported.

With the dam overflow exacerbating already heavy monsoon rains, river levels are expected to continue to rise for several days.