Hundreds of people are reported to be missing after a partially constructed hydroelectric dam collapsed in Laos.

The state news agency confirmed that 'several' people had died after the Xepian-Xe Nam Noy dam collapsed.

It happened in the Sanamxay district in the south of the country, at around 8pm local time on Monday.

Officials said five billion cubic metres of water was released, sweeping away homes.

6,600 people have been left homeless, according to the report, with six villages said to have been worst affected by flash flooding.

Prime Minister Thongloun Sisoulith and other cabinet members were reported to be heading to the flooded area to monitor rescue efforts.

Authorities in Attapeu Province have ordered emergency aid to be provided to all victims.

According to state media, construction of the $1 billion (€855 million) dam began in February 2013 and operations were due to commence later this year.