At least two Tibetans were killed and seven others wounded when Chinese border guards opened fire on them, a refugee support group has said.
The head of the UN-sponsored Tibet Refugee Reception Centre in Nepal, Loudhup Dorjee, said the alleged incident happened on Saturday.
He said about 70 Tibetan men, women and children had been trying to cross the Nangpa La pass from China into Nepal.
Forty-two managed to enter. He had no information on the fate of the others.
'Two people down'
Earlier, mountaineering website MountEverest.net carried what it said was an eyewitness report of the shooting from an unnamed climber in the area.
"Without warning, shots rang out. Over, and over and over. Then the line of people started to run uphill," the climber said.
"We saw two shapes fall. The binoculars confirmed it: two people were down, and they weren't getting up. Then more Chinese army swarmed through Advanced Base Camp."
There has been no word from the Chinese authorities.
Correspondents say hundreds of Tibetans try to cross the Himalayan border every year in an effort to flee Chinese rule.