Both teenagers are believed to be former monks at Kirti monastery and were protesting against China's occupation of Tibet, Free Tibet, which has headquarters in London, said on its Web site.
They set themselves on fire in the center of the market town Ngaba, called Aba by the Chinese, at around noon Friday.
"There are unconfirmed reports that Choepel, aged 19, died at the scene, while the condition of Khayang, also known as Lunyang, aged 18, is unknown," Free Tibet said. "There have now been seven self-immolations in Tibet since March, all within the same region."
Many Tibetans in Sichuan, a province directly east of Tibet, are angry about what they see as a move by Beijing to move ethnic Han Chinese into the majority Tibetan areas of Sichuan. Tibetans say it is a direct policy by Beijing to make Tibetans a minority in their own land.
In March 2008 four protesters in Ngaba were shot by security forces acting to contain anti-China demonstrations in the Tibetan regions, including in Lhasa in Tibet.
Earlier this month another teenager, a monk at the Kirti monastery, set himself on fire. He was badly burned but didn't die, observers said.
Free Tibet said the situation in the areas around Ngaba, and especially around Kirti Gompa Monastery, founded in 1472, has been tense since the monk Rigzin Phuntsog set himself on fire in March.
Chinese media reported at the time Phuntsog died of his injuries because local monks wouldn't allow him to remain in hospital.
After Phuntsog's death, Chinese security authorities, the army and police boosted their numbers in and around Ngaba and inside the monastery.
"At Kirti monastery, compulsory patriotic re-education, detentions and expulsions have led to a fall in the number of monks in the monastery from approximately 2,500 in March to approximately 600 now," Free Tibet said. "This is a cause of great distress."
Dozens of monks "are ready to sacrifice their lives" and many have been distributing pamphlets in the town, Free Tibet said.
Earlier this month in Serthar, another town in Sichuan, several hundred people reportedly gathered to chant "We want freedom." They also reportedly called for the return of the Dalai Lama, the spiritual head of Tibetan Buddhism who has been in self-exile in Dharamsala, northern India, since just after China's army rolled into Tibet in the later 1950s.
After the March self-immolation, the Dalai Lama -- whom the Chinese claim is urging Tibetans to revolt -- issued a written statement calling for restraint by all sides.
"I am very concerned that this situation if allowed to go on may become explosive with catastrophic consequences for the Tibetans in Ngaba," he said.