The 7.8 magnitude quake struck an area between the capital, Kathmandu, and the city of Pokhara, the US Geological Survey said.
Tremors were felt across the region, with further loss of life in India, Bangladesh, Tibet and on Mount Everest. The government has declared a state of emergency in the affected areas.
A national police spokesman told the BBC that 970 people had died in the quake, and that more than 1,700 had been injured. At least 539 people were killed in the Kathmandu valley, he added. Nepali Information Minister Minendra Rijal said there had been "massive damage" at the epicentre, from where little information is emerging.
"We need support from the various international agencies which are more knowledgeable and equipped to handle the kind of emergency we face now," he said. The US is sending a disaster response team to Nepal and has released an initial $1m (£0.7m) to address immediate needs, the US aid agency USAid has said.
Rescuers are digging through the rubble of collapsed buildings in the capital trying to reach survivors, as thousands prepare to spend the night outside as darkness fell. A number of historic buildings have been destroyed.
Among those wrecked was the landmark Dharahara tower, with many feared trapped in its ruins. After the earthquake struck, frightened residents came out into the streets. Mobile phones and other communications have been disrupted.
Source: BBC News