Police in the Nepalese capital told AFP that the exile had burned himself in an eatery near Kathmandu's Boudhanath Stupa, one of the world's holiest Buddhist shrines, terrifying tourists who were having breakfast.
"At around 8:20 am (0235 GMT), a man in his early 20s arrived at a restaurant on the premises of the Boudhanath Stupa," police spokesman Keshav Adhikari said.
"He went straight to the toilet and poured petrol over his body and set himself alight."
The monk managed to run out into the street to the foot of the stupa where police helped douse the flames before sending him to hospital in a critical condition.
The Tibetan government in exile, based in the Indian town of Dharamshala in the foothills of the Himalayas, had previously put the number of burnings since 2009 at 99, with 83 of them leading to the death of the protester.
The gruesome burnings, most of which have occurred in Tibetan-inhabited areas of
Speaking to AFP ahead of the milestone of 100 cases, Tibetan exile prime minister Lobsang Sangay blamed Chinese authorities and called for the international community to take note.
"Because there is no freedom of speech or outlet for any form of protest, unfortunately Tibetans have chosen self-immolations," he said in an interview in Dharamshala.
"To the international community I say 'stand up for Tibetans'. The Chinese government has completely militarised the Tibetan area," he added.
Beijing accuses the Dalai Lama, the Nobel Peace Prize winner and exiled Tibetan spiritual leader, of encouraging the immolations and says huge investment has brought modernisation and a better standard of living to Tibet.
The Dalai Lama fled Tibet in 1959 after a failed uprising and has since based himself in Dharamshala where Tibetans have previously marked new burnings with candle-lit vigils and prayers for the victim.
The Dalai Lama's office in New Delhi confirmed the 100th immolation attempt involved a monk. Representative Tempa Tsering called it "very unfortunate" and repeated appeals from the spiritual leader for Tibetans to end the protests.
"We feel very said that this has happened. The Tibetan leadership has been urging people to refrain from such drastic steps for long," Tsering said.
Suicide contradicts Buddhist teachings that all life is sacred, and Tibetan leaders have struggled to balance anger over Chinese rule with calls for protesters not to use such desperate measures.
The first self-immolation occurred in 2009 in the Kirti monastery in China's Sichuan province, with a pause until 2011 when they spread across the Tibetan plateau.
Nepal, home to around 20,000 Tibetans, is under intense pressure from Beijing over the exiles, and has repeatedly said it will not tolerate what it calls "anti-China activities".
"It's a sacrifice for the Tibetan people's struggle for freedom," a Tibetan community activist in Nepal said of Wednesday's protest, asking not to be named because of fears over possible reprisals.
"People are no longer afraid to go to this extent because (oppression) has crossed the limit."
The man who set himself on fire on Wednesday was expected to struggle to survive.
"His entire body was caught in the flames. At the hospital he tried to speak but couldn't," police spokesman Adhikari told AFP.
