The earthquake struck at 4:30 pm (0830 GMT) in a sparsely populated area about 84 kilometers (50 miles) west of the Tibetan capital of Lhasa, the U.S. Geological Survey said.
U.S. seismologists initially put the magnitude of the quake at 6.6, but later revised that down to 6.3.
The tremor in Tibet came after a 6.6-magnitude quake struck near China’s border with Kyrgyzstan, killing at least 72 people. Shortly thereafter, another strong earthquake rattled China’s far northwest.
Several aftershocks followed in Tibet, with one measuring 5.4.Xinhua, quoting local government officials, said many houses in Damxung county -- home to about 42,000 people -- near the quakes epicenter had collapsed, and that "more people were still buried in debris".
Soldiers and medical teams were dispatched to the area, where roads and communications had been cut off, the report said.
More deaths were reported in a neighboring county, Xinhua said, adding that an exact figure was not available.
The agency quoted Zhu Quan, director of the Tibetan seismological department, as saying authorities were still trying to determine the exact number of casualties.
The quake was felt strongly in Lhasa, Xinhua said, citing local sources.
"I was shaken for a few seconds and lamps in the office swayed. Then everything returned to normal," the report quoted one of its own Lhasa-based reporters as saying.
"Judging from how I felt, the tremor would not damage the cultural relics in Lhasa... There is no panic in the streets now. Shops remain open."
Xinhua also quoted its local staff as saying there was no visible damage to Lhasa’s world-famous Potala Palace.
Rail service between Tibet and Qinghai was operating normally, as were flights in and out of Lhasa, Xinhua said.
China suffers frequent earthquakes. An 8.0-magnitude quake struck southwestern Sichuan province on May 12, flattening entire towns and leaving more than 87,000 people dead or missing.