A new railway link from Beijing to the Tibetan capital of Lhasa has tourists from mainland China flocking to the Himalayan city, yet officials are concerned that the influx might overwhelm local cultures. The trains, which opened last July, shuttle over 6,000 people in and out of the remote city every day during peak seasons, and the number of tourists in the first half of this year nearly doubled to more than 3 million. Expenditures have also doubled to 990 million yuan (around 130.8 million U.S. dollars) in Tibet. For many Chinese tourists, Tibet's culture is the main attraction. "Tibet has very mysterious religious culture and scenery. It is very attractive to us. So I bring my whole family here to take a look at this beautiful area of our country," said Mr. Zhang. Most of the tourists are from the mainland, but nowadays, more foreigners are also heading towards the cultural hotspot after the local government made it easier for them to enter the region. Non-Chinese passport holders require an additional permit to visit Tibet, which is issued by tour agencies controlled by the government. Yet Tibetan activists have warned that tourism and migration by the Han Chinese could swamp Tibet's distinctive culture, with Tibetan people receiving less than their share of new jobs and income. Local officials said restrictions would be placed on popular areas to regulate the influx of tourists. "At present there is still room to host more tourists. Tibet has a large area and the tourists are scattered around instead of concentrated in one part of the region. The most popular place should be the Potala Palace, which you will see pretty soon. We feel the biggest pressure to keep things under control there. To better preserve the world's cultural heritage, we only sell 2,500 tickets per day," said Zhang Tianhua, deputy chief of the Tibet Environmental Protection Bureau. The Potala Palace, home to nine Dalai Lamas in history, is attracting hundreds of visitors every day. "We have been here for seven days. I began lining up to buy tickets the day before yesterday. I waited until nine o'clock last night, and it was very cold then. Finally, I got the tickets," said Mr. Mai. It costs 100 yuan (around 12.5 U.S. dollars) to get into the Buddhist landmark. The regional government will spend at least 10 million yuan (around 1.25 million U.S. dollars) each year by 2010 to promote Tibet's tourist destinations and an additional 30 million yuan (around 3.75 U.S. dollars) to develop new attractions in remote areas. China, which expects the number of tourists visiting Tibet to reach six million in 2010, is building a fourth airport at Ngari in the west, which will be the world's highest. China has poured billions of yuan into Tibet and says life has improved for most Tibetans since the Dalai Lama fled. The Dalai Lama, Tibet's god-king, fled on horseback after a failed uprising against Chinese rule in 1959 and now lives in exile in northern India. China accuses him of seeking independence for Tibet. The spiritual leader says he only wants greater autonomy for the region. Meanwhile, Chinese police have detained six protesters who unveiled a banner calling for a free Tibet on the Great Wall, a campaign group said on Tuesday. The banner read "One World, One Dream, Free Tibet" and "Free Tibet" in Chinese, the Free Tibet Campaign said. China has ruled Tibet with an iron fist since People's Liberation Army troops marched in in 1950 and has vowed to bring economic prosperity to the poor Himalayan region. "One World, One Dream" is the motto for the 2008 Beijing Olympics, which opens in a year's time. The protesters were on the Wall for about two hours before being detained and taken away, the group said. No other details were immediately available and China's Foreign Ministry said it could not comment. Beijing officials have said the Olympic torch will enter Tibet after ascending the southern slope of Mount Everest -- known in China by its Tibetan name, Qomalangma -- in Nepal. In April, China deported five Americans after they unfurled similar banners at the base of Everest.