A bus filled with people travelling to their home villages in Nepal to receive the first government payments for victims of last year’s devastating earthquake slipped off a narrow mountain road on Monday, killing at least 33 people and injuring 28 others.

The bus was heading to Kartike Deurali village, among the worst hit by the quake, which killed nearly 9,000 people in the country. The road, little more than a trail, was wide enough for only one vehicle to pass at a time and was slippery because of continuous rain.

A Nepalese home ministry official, Chiranjivi Nepal, said 33 people were killed, but injured passengers and relatives said many more may have died because the wreckage was scattered along the slope below the road and some areas were inaccessible.

“The bus stalled while climbing the hill and the driver tried to restart it, but the vehicle rolled backward and then slipped off the road,” said Kopila Gautam from a bed at the national trauma centre in Kathmandu.

Gautam said about 85 passengers were riding inside the bus and on its roof. It was also packed with bags of rice, lentils, flour and other supplies being taken to villages. Gautam was sitting on a sack of rice because there were no seats available. She said she and other survivors struggled to climb back up to the road after the crash.

Pustak Gautam, a villager who reached the site about an hour after the accident to rescue his nephew, said bodies and wreckage were scattered over a large area.

“It appeared that the bodies were ejected as the bus rolled down the slope, so I am sure more bodies will be found,” Gautam said.

Another villager, Mohan Giri, who rushed to the hospital after hearing about the accident, said the bus was unusually crowded because many people were heading from Kathmandu to their villages to receive the first government grants for earthquake victims.

The accident occurred near Khare Khola, about 80km (50 miles) east of the capital. Officials said the bus plunged off the road and rolled about 150 metres (500 ft).

Army and police personnel were searching the area for bodies.

Nepal’s mountainous terrain, extreme weather and poorly maintained roads and vehicles often make for treacherous travel conditions. Many of the bus accidents in the country happen during the monsoon season, which begins in June and ends in September.