Rescuers are searching for villagers still missing after a newly built dam broke in south-eastern Laos, flooding the surrounding countryside and killing at least 19 people.

More than 6,000 people lost their homes when the Xepian-Xe Nam Noy hydropower facility gave way on Monday, engulfing surrounding villages in south-eastern Attapeu province.

The exact number of victims is unclear. The official Lao news agency KPL said on Tuesday afternoon that hundreds of people were missing. More recent reports put the number missing in the dozens.

KPL said on Wednesday that the death toll had risen to 19.

Villages inundated with floodwaterVillages inundated with floodwater (LNT/AP)

Photos and videos posted on social media showed people sitting on rooftops to escape the surging water, while others were carried to safety or rescued by boat. State media said helicopters were being used to rescue people.

SK Engineering & Construction, one of two South Korean partners in the project, said the top of one of five auxiliary earth-fill dams at the project “got swept away” on Sunday night after heavy rain.

But Korea Western Power, which was due to operate the hydroelectric power plant after its completion, said problems first emerged on Friday when workers discovered the dam’s centre had sunk 4.3in.

Repair work for the earth-fill dam was hampered by heavy rain and damaged roads, and the situation worsened on Monday as water cascaded out of the reservoir, flooding seven out of 12 villages in the area, SK E&C said.

It was helping to evacuate and rescue residents while also trying to contain further damage.

Residents are evacuated in the floodwaterResidents are evacuated in the floodwater (Attapeu TV/AP)

The government declared the area a disaster zone and officials rushed to the site, it said.

Continued heavy rain and strong winds forecast for the area could hinder rescue efforts, and risks from flooding persisted in the mountainous region.

Provincial authorities issued a call for emergency aid — clothing, food, drinking water, medicine, cash and other items — from the “party, government organisations, business community, officials, police and military forces and people of all strata”.

The International Red Cross said food was a concern because village food supplies were drenched in the floodwater. It was arranging for purification units to be sent to the area to ensure supplies of clean drinking water.

The presidential office in South Korea said President Moon Jae-in had ordered an emergency relief team to help with the disaster.

SK E&C sent its president to Laos and set up an emergency team in Seoul, South Korea’s Yonhap News agency reported.

The £775 million project encompassing several river basins in a remote corner of south-eastern Laos is the first hydroelectric dam built by a South Korean company, and it was unclear how severe the damage would be to the overall plan.

The dam was due to begin operating in 2019, with 90% of the power generated going to Thailand.