Several travel agencies in China are reporting that foreigners have been banned from traveling to the Tibet Autonomous Region, the Chinese name for Central Tibet.

The agencies claim the ban, imposed by the Chinese National Tourist Office (CNTO), will last at least through June, and perhaps continue indefinitely.

The latest we've heard is that it will last until November, said Marilyn Downing Staff, founder and president of Asia Transpacific Journeys.

Downing Staff said she's had to re-route several travelers to other parts of China that still have a Tibetan flavor.

Now, of course, is the high season and it's unfortunate on so many fronts, she added. But one thing to keep in mind in Tibet is the tourism is now driven by the Chinese, so the few westerners that turn up in Tibet are not exactly driving the economy.

The ban comes amidst increasing concerns over self-immolations. At least 38 Tibetans have set themselves on fire in Tibetan regions since 2009 in protest of Chinese rule. In late May, two Tibetans performed the act in front of the Jokhang, the holiest temple of Tibetan Buddhism in the center of Lhasa. It was the first recorded attempt in Lhasa, the capital and hub of regional tourism.

Chinese authorities claim that the immolations are orchestrated from the outside and incite separatism. Followers of spiritual leader Dalai Lama, based in northern India, say protesters are driven to these extreme measures because they cannot tolerate Beijing's sanitization of local religion and culture.

Foreigners were forbidden in Tibet from late February to early April during the anniversary of large protests against Chinese rule.

The latest ban comes as Tibetans prepare for the month-long festival of Saga Dawa, marking three important events in Buddha's life: his birth, nirvana, and parinirvana (death). This year, the festivities began on June 4, the anniversary of the Chinese government crackdown on the Tiananmen Square protests. The Saga Dawa festivities typically draw thousands of tourists and fall during the region's peak tourism season.

China enforced a similar ban on foreigners last year around the same time and has done so periodically during religious holidays or times of unrest.

Even in normal times, all foreign tourists in Tibet are closely monitored by the government and must apply for a special visa. Any foreign tour operator traveling through the region must first make arrangements through a Chinese firm and be accompanied by a government-appointed guide.

Tibet received about 21.25 million domestic and foreign tourists between 2006 and 2010, generating some $3.58 billion in income for the autonomous region. A staple of the region's economy, Tibet set a goal to increase tourism revenue between 2011 and 2015 by over 20 percent of its gross domestic product.

If periodic closures continue, they will struggle to meet that goal.

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