Nepal's prime minister on Sunday appealed for $2 billion to rebuild his country, shattered by two massive earthquakes in three weeks that have killed thousands and devastated the impoverished nation's infrastructure.

On April 25 a 7.8-magnitude quake, the deadliest to hit the country in more than 80 years, killed more than 8,500 people and destroyed half a million homes.

That was followed weeks later by a second massive tremor that triggered landslides and brought down houses, triggering fresh misery for people still traumatised by the earlier quake.

The disasters have also left their mark on the impoverished Himalayan nation's infrastructure and development.

Prime Minister Sushil Koirala, whose year-old government has faced criticism over the speed of its response to the quakes, said Sunday that the administration has set up a national rehabilitation and reconstruction fund, and urged donors to help.

"Our target is to raise $2 billion. Government has earmarked $200 million as a seed money for the fund with a request to donors communities and private sector to make necessary contribution," Koirala said.

"Rehabilitation and reconstruction is very important for us and we hope our friends will come with a large heart to assist."

More than 20 countries have been involved in relief efforts since the first quake struck, sending rescuers to help search for survivors and aid in relief efforts.

Earlier this month the UN said it had received just $22 million of the $415 million it had appealed for following the disasters.

A US marine helicopter delivering aid went missing last week and was found crashed in a remote forest on Friday. According to the Nepalese army, the bodies of eight servicemen on board, six American and two Nepalese, were recovered and brought to the capital Kathmandu on Sunday.

Aid agencies have warned of a race against time to provide shelter and bring relief to victims before the approaching monsoon season triggers more landslides and blocks access to quake-hit villages located along the Himalayan nation's hills and mountains.

Koirala's government has said it was overwhelmed by the scale of the April 25 earthquake, and that the country was unprepared for the second tremor.