Chanting of red-robed monks and nuns rang out from Himalayan hilltop forested temples in India, home to the Dalai Lama since he and thousands of other Tibetans fled Chinese troops who crushed an uprising in their capital Lhasa in 1959.

"I am just a simple Buddhist monk; I don't normally engage in birthday celebrations," the Dalai Lama said in a message, thanking those marking it with him for using the opportunity "to cultivate peace of mind and compassion".

Dressed in traditional robes and a flowing yellow wrap, he walked with the aid of two monks while flashing his trademark beaming smile to thousands of followers.

Beijing condemns the Nobel Peace Prize winner -- who has led a lifelong campaign for greater autonomy for Tibet, a vast high-altitude plateau -- as a rebel and separatist.

Alongside the celebrations, however, is the worry for Tibetans in exile that China will name its successor to bolster control over the territory it poured troops into in 1950 and has ruled ever since.

That raises the likelihood of rival challengers to the post; one by self-declared atheist Beijing, the other by the Dalai Lama's office based in neighbouring India, a regional rival of China.

- 'Good heart' -

The celebrations on Sunday are the culmination of days of long-life prayers for Tenzin Gyatso, who followers believe is the 14th reincarnation of the Dalai Lama, a man whose moral teachings and idiosyncratic humour have made him one of the world's most popular religious leaders.

"While it is important to work for material development, it is vital to focus on achieving peace of mind through cultivating a good heart and by being compassionate, not just toward near and dear ones, but toward everyone," he said in his birthday message.

"Through this, you will contribute to making the world a better place."

The celebrations also included his key announcement that, after being inundated with messages of support from fellow Tibetans both inside and in exile, the spiritual institution will continue after his death.

He said he had received appeals from followers from across the Himalayan region, Mongolia and parts of Russia and China.

The seemingly esoteric matters of reincarnation have real-world political consequences, with Tibetans fearing his death will mark a major setback in his push for more autonomy for the Himalayan region.

The Dalai Lama said his India-based office alone would "exclusively" identify that successor -- prompting a swift and sharp reply from China that the reincarnation "must be approved by the central government" in Beijing.

China said the succession would be carried out "by drawing lots from a golden urn", foreign ministry spokeswoman Mao Ning told reporters on Wednesday.

That urn is held by Beijing, and the Dalai Lama has warned that, when used dishonestly, it lacks "any spiritual quality".

Indian Prime Minister Narendra Modi offered effusive birthday greetings on Sunday, calling the Dalai Lama an "enduring symbol of love".

India and China are intense rivals competing for influence across South Asia, but have sought to repair ties after a 2020 border clash.

- 'Freedom and dignity' -

US Secretary of State Marco Rubio also said in a statement that Washington was "committed to promoting respect for the human rights and fundamental freedoms of Tibetans".

Among the crowds attending the celebrations was Hollywood star Richard Gere, a longtime backer of the Tibetans in exile, who on Sunday said the Dalai Lama "totally embodies selflessness, complete love and compassion and wisdom".

Messages of support were also given by former US presidents Bill Clinton and George W. Bush, as well as Barack Obama, who said the Dalai Lama had shown what it means to "speak up for freedom and dignity".

The ceremony ended with the Dalai Lama eating a slice of cake and thousands singing "happy birthday".

No details have been released for the future succession.

All so far have been men or boys, often identified as toddlers and taking up the role only as teenagers.

The current Dalai Lama, himself identified in 1937, has said that if there is a successor it will come from the "free world" outside China's control.

In a speech to followers on Sunday, the Dalai Lama said his practice of Buddhism meant he had dedicated his life towards seeking compassion.

"I'm now 90 and... when I reflect on my life, I see that I have not wasted my life at all", he said, speaking in Tibetan.

"I would not have regrets at the time of my death; rather I would be able to die very peacefully."