Many others were trapped as dozens of aftershocks shook the remote region.
Rescue workers climbed mounds of broken bricks, some using ladders in heavily damaged villages, as they searched for survivors.
Videos posted by China's Ministry of Emergency Management showed two people being carried on stretchers by workers treading over the debris from collapsed homes.
At least 188 people were injured in Tibet on the Chinese side of the border, the official Xinhua News Agency said.
Chinese authorities say a strong earthquake has flattened hundreds of houses in Tibet. (AP PHOTO)
More than 1000 homes were damaged in the barren and sparsely populated region, state broadcaster CCTV reported.
In video posted by the broadcaster, building debris littered streets and crushed cars.
People in northeastern Nepal strongly felt the earthquake but there were no initial reports of injuries or damage, according to the country's National Emergency Operation Centre.
The area around Mount Everest, about 75km southwest of the epicentre, was empty in the depth of winter when even some residents move away to escape the cold.
The quake woke up residents in Nepal's capital of Kathmandu - about 230km from the epicentre - and sent them running into the streets.
The US Geological Survey said the earthquake measured magnitude 7.1 and was relatively shallow at a depth of about 10km.
China's Earthquake Networks Centre recorded the magnitude as 6.8.
Shallow earthquakes often cause more damage.
The epicentre was in Tibet's Tingri county, where the India and Eurasia plates grind against each other and can cause earthquakes strong enough to change the heights of some of the world's tallest peaks in the Himalayan mountains.
There have been 10 earthquakes of at least magnitude 6 in the area where Tuesday's quake hit over the past century, the USGS said.
About 150 aftershocks were recorded in the nine hours after the earthquake, and the Mount Everest scenic area on the Chinese side was closed.
Chinese leader Xi Jinping called for all-out efforts to rescue people, minimise casualties and resettle those whose homes were damaged.
More than 3000 rescuers were deployed, CCTV said.
Vice Premier Zhang Guoqing was dispatched to the area to guide the work, and the government announced the allocation of 100 million yuan ($A21.7 million) for disaster relief.
About 6900 people live in three townships and 27 villages within 20km of the epicentre on the Chinese side, state media said.
The average altitude in the area is about 4200 metres, the Chinese earthquake centre said in a social media post.
On the southwest edge of Kathmandu, a video showed water spilling out into the street from a pond in a courtyard with a small temple.
"It is a big earthquake," a woman can be heard saying.
"People are all shaking."
