Thumping drums and deep horns reverberated from the Indian hilltop temple, as a chanting chorus of red-robed monks and nuns offered long-life prayers for Tenzin Gyatso, who followers believe is the 14th reincarnation of the Dalai Lama.

Looking in good health, dressed in traditional maroon monk robes and a flowing yellow wrap, he led prayers -- days after confirming that the 600-year-old Tibetan Buddhist institution will continue after his death.

Many exiled Tibetans fear China will name its own successor to the Dalai Lama, to bolster control over a territory it poured troops into in 1950 and has ruled ever since.

"So far, I have done my best and with the continued blessings of Avalokiteshvara (a Buddhist spiritual protector), I hope to live another 30 or 40 years, continuing to serve sentient beings and the Buddha Dharma", he said, referring to the teachings of the Buddha.

Followers of the Dalai Lama laud his tireless campaign for greater autonomy for Tibet, a vast high-altitude plateau about the size of South Africa.

- 'Experience happiness' -

But speaking at the main temple in the Indian Himalayan town where he has lived for decades -- after Chinese troops crushed an uprising in the Tibetan capital Lhasa in 1959 -- he offered teachings to a far wider audience.

"In my life, I have encountered people from all walks of life, those with faith in religion and others with no interest in it at all. This is only natural, as individuals have different mental dispositions", he said, speaking in Tibetan.

"Yet, the common desire shared by all, including the Tibetan people, is the wish to avoid suffering and to experience happiness."

The charismatic Buddhist had previously said the institution would continue only if there was popular demand -- and his confirmation on Wednesday it would has reassured followers around the globe.

He said he had received multiple appeals from Tibetans in Tibet and in exile, as well as from Buddhists from across the Himalayan region, Mongolia and parts of Russia and China.

He said responsibility for identifying the 15th Dalai Lama "will rest exclusively" with his office, the India-based Gaden Phodrang Trust.

Self-declared atheist and Communist China, which condemns the Nobel Peace Prize winner as a rebel and separatist, issued a swift response.

China said on Wednesday that the reincarnation of the Dalai Lama "must be approved by the central government" in Beijing, and that it would be carried out "by drawing lots from a golden urn", foreign ministry spokeswoman Mao Ning told reporters.

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

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

New Delhi's foreign minister said it had "always upheld freedom of religion for all in India and will continue to do so".

- 'Struggle' -

The birthday celebrations have also been a time for reflection on an inevitable future without the Dalai Lama.

"Seeing him turn 90 today fills me with happiness, but also a deep sadness," said Dorje Dolma, 27, who fled Tibet to India.

"His Holiness has always felt like a father figure to me," she added. "His good health brings me joy, but his age sometimes worries me."

Hollywood star Richard Gere, a longtime backer of the Tibetans in exile, has been among the tens of thousands taking part in days of celebrations.

"There's something about this Tibetan cause that touches people, and certainly, a central part of that is His Holiness the Dalai Lama," Gere said during celebrations on Thursday.

"Which begs the question: What do we do when we don't have His Holiness to open those doors? He's not there to carry us. And we struggle with that, all of us now."