A photo shows the Potala Palace in Lhasa City of southwest China's Tibet Autonomous Region. [Photo: Chinanews.com]

Police in Lhasa, capital of Tibet, have begun a campaign to crack down on scalpers and unauthorized tour guides at the 1,300-year-old Potala Palace.

May to October is the busy season for visitors and the campaign will continue until the end of the season, police told Xinhua.

A UNESCO World Heritage Site, the Potala Palace in Lhasa was built by Tibetan King Songtsa Gambo in the seventh century and expanded in the 17th century by the Dalai Lama. It received more than 900,000 visitors last year.

To minimize damage to the wood and earth structure, the number of visitors is limited to 5,000 a day. Visitors need to book in advance. That is one of the reasons why scalpers and unauthorized tour guides exist.