Tibetan new year is usually a time for festivities in China's ethnically Tibetan areas, but this year some are choosing not to celebrate after deadly unrest and a huge security clampdown.

Chinese authorities have implemented what some experts say are unprecedented measures of control on vast swathes of ethnically Tibetan regions following a wave of self-immolations by Buddhist monks and nuns.

Last month, police shot and killed at least two Tibetans in the southwestern province of Sichuan -- which borders the Tibet autonomous region (TAR) and has a large population of ethnic Tibetans.

Tibet's exiled government has called on Tibetans not to celebrate their new year -- or Losar -- which begins on Wednesday, and instead observe traditional and spiritual rituals for those who have died.

"Tibetans would now be getting ready for parties, family get-togethers, lots of food and drink," said Kate Saunders, spokeswoman for the International Campaign for Tibet (ICT), which has exile sources with contacts on the ground.

"But this year... Tibetans have decided not to celebrate but to honour those who have died, particularly through self-immolations, by offering prayers and paying solemn respect to the traditions of their culture."

At least 22 Tibetans have set themselves on fire in China over the past year in protest against perceived repressive Chinese rule.

Authorities have imposed virtual martial law in Sichuan and other areas, increasing their surveillance of monasteries and cutting some phone and Internet communications.

Human Rights Watch has reported that authorities have detained large numbers of Tibetans with valid passports for political re-education after they returned from a visit to India to listen to religious teachings.

Robbie Barnett, a Tibet expert at Columbia University, said authorities in the TAR in particular had markedly tightened regulations.

Chinese authorities have stopped foreign journalists from going to the affected areas, making independent attempts to verify the situation there nearly impossible.

"I don't think this type of mass internment for political reasons -- as opposed to criminal reasons -- has happened for decades. These are laypeople who have not been accused of anything forbidden in Chinese law," said Barnett.

Barnett added that officials were also being permanently stationed in some monasteries, where a notional self-rule system had previously been in place that saw monks run supervision committees and report to higher authorities.

"This switch from indirect to direct rule means they have abandoned the attempt to maintain an appearance of non-intervention," he said.

"Now they're going to have a new committee with laypeople who are officials, and there has never been a precedent for this in China's religious policy."

Many Tibetans in China complain of religious repression, as well as a gradual erosion of their culture, which they blame on a growing influx of majority Han Chinese in the areas they live in.

China, however, denies this and says Tibetans are leading better lives than ever before thanks to huge investment in infrastructure, schools and housing.

In a report on Losar, the state-run Xinhua news agency said Lhasa's major commercial streets had been crowded with shoppers buying beef, yak butter and tea bricks for the holiday, effectively denying reports of non-celebrations.

It added that many residents in Tibet's capital were also "trying traditions from other parts of China, as the gap between the plateau region and China's interior regions narrows."

"Pairs of red couplets printed with Tibetan words of greeting, a symbol of New Year imported from other parts of China, are gaining popularity in Lhasa," it said.

Barry Sautman, a Tibetologist at the Hong Kong University of Science and Technology, said Tibetans in some parts of China -- such as Sichuan -- had tended to celebrate the Chinese Lunar New Year instead of Losar in the past.

As a result, the question of whether to celebrate Losar has taken on an extra dimension in those areas.

"If they did celebrate Losar in an area where they didn't traditionally celebrate it, that might be viewed as a kind of re-emphasis of their Tibetan-ness," he said.

"On the other hand, if the exile government recommended that people don't celebrate Losar to express mourning or opposition, and if they went ahead and celebrated, that might be interpreted in a different way."