At least 50 people have been reported dead in Nepal and 17 in India after the second powerful earthquake to hit the region
The latest earthquake struck near the town of Namche Bazaar and sent thousands of panicked residents on to the streets of Nepal's capital, Kathmandu.
The 7.3 magnitude quake struck at 12.35pm local time and was centred 76km east of Kathmandu, in a rural area close to the Chinese border.
It came two weeks after more than 8000 died in a 7.8 quake, on 25 April, taking the overall death toll to more than 8,200, and compounding the challenge of reaching remote mountain communities in desperate need of shelter, food and clean water.
The latest quake was felt in northern India, Tibet and Bangladesh. India's home ministry said 16 people had been killed in the state of Bihar, and one more in Uttar Pradesh. Officials in China said one person was confirmed dead in Tibet.
But people are still buried under rubble, and the number of dead is expected to rise. Many people have again been sleeping outside, too scared to stay at home.
UNICEF communications director Rose Foley in Kathmandu said the aid agency will ramp up its response to help children who are already in "huge need of humanitarian aid."
Many children are too frightened to return to their homes so UNICEF has set up shelters as well as providing relief supplies, Ms Foley told Morning Report.
Rescue helicopters have been sent to districts east of Kathmandu, that are believed to be worst hit. Police in Charikot, 80km north-east of the capital, said 20 people had died there.
Aid agencies say the latest quake has set back the relief effort from the first earthquake, though Kai Tabacek Oxfam in Britain said the supplies and resources were there so the relief operation was able to quickly swing back into action.
A spokesman for Nepal's government said 31 of the country's 75 districts had been affected.
Prime Minister Sushil Koirala called for "courage and patience" and urged all those who had assisted Nepal since the 25 April quake "to once again extend your helping hand".
At least four people were killed in the town of Chautara, east of Kathmandu, where a number of buildings are reported to have collapsed.
The International Organisation for Migration said bodies were being pulled from rubble there.
Krishna Gyawali, the chief district officer for Chautara, said there had been a number of landslides.
Landslides were also reported by Save the Children in Sindhupalchok and Dolakha. A spokeswoman told the BBC its staff had been "dodging huge rocks rolling off the hillside".
Meanwhile, American officials say a US Marine Corps helicopter helping with recovery operations has gone missing. Reports say there were eight people on board; six marines and two Nepalese soldiers.
Officials said the helicopter was in the vicinity of Charikot village, which was badly hit by the latest earthquake.
Tuesday's earthquake is likely to be one of the largest to hit Nepal, which has suffered hundreds of aftershocks since 25 April.