It was once a mystical mountain enclave closed to outsiders and ruled by red-robed Buddhist monks, but the number of tourists visiting Tibet is set to double to six million between now and 2010.

The introduction of regular flights as well as a high-tech rail link to the Tibetan capital, Lhasa, that started a year ago, has seen tourists arrive in droves to the city where historically, neither foreigners or Chinese dare enter.

The opening up of Tibet is a contentious issue. Beijing says it is bringing prosperity to a traditionally impoverished area, and has engaged in a huge building programme. According to a regional government document, tourism could bring at least six billion yuan (£400m) or about 12 per cent of the region's gross domestic product.

Tibetan activists fear that local people will receive less than their share of new jobs and income, and that tourism and migration by Han Chinese could swamp the area's distinctive culture.

Lhasa has changed profoundly since Chinese troops entered in 1950 and started to impose the dominant Han culture on the ancient territory. Beijing says Tibet has been part of China for centuries and accuses the Dalai Lama, who left after a failed uprising in 1959, of agitating for independence.

In the first four months of this year, 198,000 tourists travelled to Tibet and according to the official Xinhua news agency, the tourist tally is set to reach three million this year, yielding £230m in revenues.

Many of them arrive via the new rail link, which cost £2bn to build. Along a 710-mile track across the area known as the Roof of the World, it carries passengers on a 48-hour voyage from Golmud in Qinghai province.

The regional government is planning to spend at least 10 million yuan a year by 2010 to promote Tibet's tourist destinations and 30 million yuan to develop remote areas, Xinhua said.