Tibet's architectural gem, the Potala Palace, saw 4.04 million tourists and believers in Buddhism over the past five years, local cultural heritage authorities announced Wednesday.

The tourist numbers received a boost after the Qinghai-Tibet railway was put into service in July 2006, as the daily number of visitors allowed to tour the Potala Palace was raised to 2,300 from 1,500.

Further, the number of tourists exceeded 1 million in 2007, up 56 percent from one year earlier. But it fell sharply to about 478,300 in 2008 because of the deadly riots in Lhasa on March 14, 2008.

However, tourism regained momentum over the past two years, with tourist numbers climbing to 780,000 in 2009 and more than 1 million last year.

The Potala Palace, first built in the 7th century, was the winter palace of the Dalai Lamas and is today a World Cultural Heritage site.

Norbu Linkag, the summer palace of Dalai Lamas and also a World Heritage site, received 2.3 million tourists and Buddhist pilgrims between 2006 and 2010, according to the Tibet Autonomous Regional Bureau of Cultural Heritage.