The death toll from severe flash floods in a mountainous region of Nepal has risen to at least 157, police said.

Hundreds of people remain unaccounted for following the disaster, which caused widespread destruction along the Bhotekoshi River near the border with China.

Those reported missing include hundreds of foreign tourists as well as Nepalese travellers and members of the police and security forces.

Homes, roads, bridges and hydropower facilities were destroyed as the water surged mountain valleys, with Nepal's Rasuwa district particularly badly affected.

So far, neighbouring China has reported three deaths and 265 people missing in south-western Tibet.

What triggered the flash floods on Wednesday morning remains unclear. One hypothesis being considered by authorities is the outburst of a glacial lake in Tibet, in which a lake fed by melting glaciers suddenly releases a massive volume of water.