A vast three-kilometre-long section of land, with a volume of two million cubic metres, slid down a slope and buried the workers' camp in Maizhokunggar county, east of the Tibetan capital Lhasa, the official Xinhua news agency said.
A total of 1,000 police, firefighters and doctors were sent to the disaster site, at an altitude of 4,600 metres, the agency said, with 200 vehicles and 15 dogs, and sets of life-detecting equipment.
State broadcaster CCTV quoted a member of the Chinese People's Armed Police on the scene as saying that "the situation looks serious, the collapsed area is three or four square kilometres".
The landslide brought massive rocks which smashed the workers' camp area and sliced a huge excavator into two, Xinhua said citing witnesses.
Rescuers have so far found no signs of the 83 trapped workers. The rescue would be very difficult due to the size of the affected area, Xinhua cited a fire department official as saying.
The workers were from a subsidiary of the China National Gold Group Corporation, a state-owned company and the nation's biggest gold miner by output.
Almost all of them were Han Chinese, the national ethnic majority, with only two of them ethnic Tibetans, Xinhua added. Most were migrant workers from the provinces of Yunnan, Guizhou and Sichuan.
China's new president Xi Jinping, who is currently visiting the Republic of Congo in Africa, and new premier Li Keqiang had ordered "top efforts" to rescue the victims, Xinhua added.
"Xi and Li have told local authorities to spare no efforts to rescue the buried and prevent secondary disasters," it said.
A worker at a hospital in the county reached by AFP late on Friday said it had not yet received any casualties but staff were "making preparations".
A female member of staff who answered the phone at the county government office said she was not clear about the situation and hung up.
The Lhasa city government and China National Gold Group Corporation did not immediately answer calls late Friday.
The landslide struck at about 6:00 am local time, but Xinhua's first news reports about it ran more than 15 hours later.
Mountainous regions of Tibet are prone to landslides, which can be exacerbated by heavy mining activity.
Han Chinese have been increasingly moving into historically Tibetan areas, and many Tibetans in China say their culture is being eroded.
Beijing rejects criticism of its rule, pointing to huge ongoing investment it says has brought modernisation and better standards of living to Tibet.
In recent years China has discovered huge mineral resources in Tibet, including tens of millions of tonnes of copper, lead and zinc, and billions of tonnes of iron ore, according to state media reports.
The reserves are estimated to be worth more than $100 billion, Xinhua reported in 2011, citing government statistics. It quoted a local official saying that the purpose of mining was to "benefit the local people".
But mining developments can lead to accusations of exploitation.
In 2010, at least four Tibetans may have been killed and 30 others hurt when Chinese police fired on crowds protesting the expansion of mine operations blamed for environmental damage, US-based Radio Free Asia reported.
The demonstrators, in a Tibetan area of Sichuan province, complained that stepped-up Chinese gold-mining operations had brought large numbers of people and heavy machinery to the area, damaging farmland and the local grassland habitat, it said.
Tensions in the region remain high. Since 2009 around 110 ethnic Tibetans have set themselves on fire in protest at Chinese rule.
Beijing accuses the exiled Tibetan spiritual leader the Dalai Lama, who fled after a failed uprising in 1959, and his "clique" of inciting the burnings to push a separatist agenda.
But the Nobel peace laureate says he is seeking greater autonomy for the region, rather than independence.