The death toll in Nepal from weekend floods and landslides rose to six, officials said Monday, as rescuers continue to search for 28 missing people.

"Rescuers are still searching for those who have remained out of contact due to floods and landslides since Saturday," Dhruba Bahadur Khadka, spokesperson of the National Disaster Risk Reduction and Management Authority, told AFP.

A worker at a hydropower project on the Hewa River in Nepal's eastern Sankhuwasabha district was found dead, while 17 other staff have been missing since Saturday evening, Khadka said.

He said the number of confirmed dead had risen to six.

Every June to September, monsoon rains wreak widespread death and destruction across the South Asian country, but the number of fatal floods and landslides has increased in recent years.

Experts say climate change and greater road construction could be worsening these disasters.

Krishna Kumar Tamang, mayor of Chainpur municipality in Sankhuwasabha, told AFP he feared more damage from the ongoing rains.

"We are doing whatever we can do to rescue and provide the affected people relief," he told AFP. "The rainfall has not stopped. More settlements are at risk due to floods and landslides."

Three others died in landslides in neighbouring Taplejung district, officials said.

Nepal's army said on Monday that it rescued 12 people by helicopter after they were trapped by landslides in Panchthar district, where officials said two people had died.

Forecasters warn river levels will continue to rise for the next three days.