Nepal’s prime minister has declared three days of national mourning for the victims of Saturday’s devastating earthquake which has left at least 4,700 people dead.

Nepal's prime minister has declared three days of national mourning for the victims of Saturday's devastating earthquake which has left at least 4,700 people dead.

Rescue operations were continue on Tuesday, with helicopters ferrying the injured and delivering emergency supplies to remote villages near the epicenter.

Prime minister Sushil Koirala also thanked donors in a televised address to the nation.

He had earlier warned that the number of people killed in the country's worst earthquake in decades could reach 10,000.

With the UN estimating eight million people have been hit by the disaster, Koirala said getting help to some of the worst affected areas was a "major challenge".

He said authorities were overwhelmed by appeals for help from remote Himalayan villages left devastated by the 7.8-magnitude earthquake.

Aid workers who had reached the edges of the epicentre described entire villages reduced to rubble.

"In some villages, about 90 percent of the houses have collapsed. They're just flattened," said Rebecca McAteer, a US physician who went to the earthquake zone from the distant Nepal hospital where she works.

Two rescue helicopters on Tuesday reached Ranachour village, in Gorkha district, evacuating eight women, two of them clutching babies, and a third heavily pregnant, to the nearby town of Gorkha.

"There are many more injured people in my village," said Sangita Shrestha, who was pregnant and visibly downcast as she got off the helicopter.

In Barpak, further north, rescue helicopters were unable to find a place to land. On Tuesday, soldiers had started to make their way overland, first by bus, then by foot.

Helicopters dropped food packets in the hope that survivors could gather them up.

Meanwhile, an avalanche stuck a village on Tuesday in Rasuwa district, a popular trekking area to the north of Kathmandu.

Uddhav Bhattarai, the district governor, said up to 250 people were missing.