Some 50,000 people have been forced to flee after monsoon rains washed away a dam in southern Nepal and were taking refuge in makeshift shelters, schools and temples, an official said Wednesday.

The dam on the Saptakoshi river burst Monday following heavy downpours, government disaster management official Suman Ghimire said, adding that rescue teams of locals and security personnel were helping victims.

"Five villages have been flooded and the residents have been evacuated," said Ghimire.

Nepal's new Maoist Prime Minister Prachanda was travelling to the flooded Sunsari district bordering India, 200 kilometres (125 miles) southeast of the capital Kathmandu to check on rescue efforts, Ghimire said.

"We think people may have been killed but we have not been able to verify the number," the official said.

The annual June-to-September monsoon causes scores of deaths in the mountainous country through flooding and landslides.