Passenger numbers at Tibet's airports surged by 21.1 percent year on year to about 2.22 million in 2012, according to regional civil aviation administration figures available on Thursday. The five airports in the autonomous region in southwest China handled about 21,000 flight landings and take-offs last year, an annual growth of 30.6 percent. This was due to a boost in tourism, a spokesman for the aviation administration said. More than 10 million tourists visited Tibet last year and the administration opened eight new air routes, the spokesman said. He added that a new airport is expected to start construction in Nagqu in the north of Tibet this year. This will further improve the aviation network of airports in the vast plateau region. Seven airline companies are operating 37 routes linking the region dubbed "the roof of the world" with 21 Chinese cities, as well as Kathmandu, capital of Nepal. In 2012, the regional government announced the establishment of special funds to bolster civil aviation in Tibet, with 100 million yuan (16 million U.S. dollars) to be pooled annually to support the maintenance and expansion of airports and airline companies in Tibet. In June 2012, the Tibet regional government reached an agreement with the China Civil Aviation Administration to launch air routes to southern and western Asian countries. Tibet's airports are expected to handle 4 million passengers in 2015, which will double the figure in 2012.