At least 66 people have been killed in Nepal since early on Friday as persistent downpours triggered flooding and landslides, closing major roads and disrupting domestic air travel, officials said on Saturday.

The death toll could rise, they added, with another 69 people reported missing, and 60 injured since Friday morning, home ministry official Dil Kumar Tamang told Reuters.

Most of the deaths took place in the Kathmandu Valley, which is home to four million people and the country’s capital, where the flooding brought traffic and normal activity to a standstill.

Rescue workers used helicopters and rubber boats to help people stranded on rooftops or elevated ground as some parts of Kathmandu reported up to 322.2 millimetres of rain over the last day.

Most rivers in the Himalayan nation have swollen, spilling over roads and bridges, authorities said, after nearly a week’s delay in the retreat of South Asia’s annual monsoon rains brought torrential downpours across the region.

Police were working to clear debris and reopen roads after landslides blocked highways in 28 places, said police spokesperson Dan Bahadur Karki.

The earliest let-up in the rains might not come until Sunday, said Binu Maharjan, a weather forecasting official in Kathmandu, who said a low-pressure system over parts of neighbouring India had caused this year’s extended rains.

“Heavy rains are likely to continue until Sunday morning and weather is likely to clear after that,” Maharjan told Reuters.

Most central and eastern areas had received moderate to extremely heavy rainfall, ranging from 50mm to more than 200mm, she added, with moderate levels recorded elsewhere.

International flights are operating, but many domestic flights have been disrupted, said Rinji Sherpa, a spokesperson for Kathmandu Airport.

The Koshi River in the southeast, which causes deadly floods in India’s eastern neighbouring state of Bihar almost every year, was running above the danger level at 450,000 cusecs, versus the normal figure of 150,000 cusecs, one official said.

A cusec is a measurement of water flow equivalent to one cubic foot a second.

The river level is still rising, added Ram Chandra Tiwari, the area’s top bureaucrat.

Hundreds of people die in the monsoon season every year in the landslides and flash floods common in the mountainous nation.

Authorities said at least 254 people have died and 65 missing in landslides, floods and lightning strikes since mid-June when the annual monsoon rains began.