Five Tibetans including three teenage monks and a young mother have set themselves on fire to protest against Chinese rule over the Himalayan region, according to Tibetan rights groups. At least two of them have died.

The five self-immolations – the most ever recorded by Tibetans in one day – came a day before Thursday's start of a week-long Communist party congress in Beijing that will usher in China's new political leadership.

The three monks set themselves on fire at about 3pm outside a police station in Ngaba county, Sichuan province, while calling for freedom and the return of their exiled spiritual leader the Dalai Lama, according to the non-profit broadcaster Radio Free Asia.

One of the monks, 15-year-old Dorje, died at the scene, while the other two – 16-year-olds Dorje Kyab and Samdrub – were taken to a county hospital by security officers. Their current condition is unknown. The London-based group Free Tibet called the incident "the first triple self-immolation protest to happen in Tibet".

About three hours later, a 23-year-old nomadic woman in Rebkong county, Qinghai province, burned herself to death, leaving behind a young son. "Tamdin Tso siphoned petrol from a motorbike and set fire to herself in the family's winter pasture," Free Tibet reported on its website. "Her body was taken back to the family home where local people gathered to pray."

About 3,000 local Tibetans took to the streets to protest against Chinese rule after the woman died, according to Radio Free Asia. The broadcaster also wrote that a fifth Tibetan self-immolated in the Tibet autonomous region's Nagchu prefecture on Wednesday, but did not provide a name.

The reports could not be independently verified. Calls to the Ngaba town police station rang unanswered.

According to the New York-based International Campaign for Tibet, 68 Tibetans have self-immolated since 2009, 55 of whom have died, and nine of whom were women. Two-thirds have been under 25; the oldest was in his 60s. They have come from urban and rural areas in the Tibetan autonomous region itself as well as nearby Gansu, Qinghai and Sichuan provinces.

According to Tsering Tsomo, executive director for the Tibetan Centre for Human Rights and Democracy in Dharamsala, India, Ngaba has faced tight restrictions since large-scale protests gripped the county in 2008. Tibetans are not allowed to freely enter or exit the area, she said. Authorities require locals to register with government-issued IDs before they can purchase flammable liquids.

"It's really surprising for us that these three immolations happened in Ngaba, given the internal surveillance in the area and the government lockdown there," she said. "We are clueless right now."

The government has introduced a barrage of new country-wide regulations for the 18th party congress, a once-in-a-decade leadership transition that began on Thursday morning. The internet in Beijing has slowed to a crawl, construction projects have been put on hold, and hotels have been instructed to inspect guests' luggage by hand.

Authorities have already embarked on a "patriotic education" campaign in Tibet, forcing monks to hang portraits of Communist party leaders on monastery walls. They have offered cash rewards as high as $30,000 (£19,000) to locals for information on self-immolations and protests.

Despite the security measures, reports of self-immolations have escalated in the past few weeks. Last month, seven Tibetans killed themselves in seven days. On Sunday, a 25-year-old artist in Tongren, Qinghai province, burned himself to death.

A 43-year-old blogger named Gudrup who self-immolated in early October left behind an article. "We are declaring the reality of Tibet by burning our own bodies to call for freedom of Tibet," it said. "We will win the battle through truth, by shooting the arrows of our lives, by using the bow of our mind."

Tibetan activists call the persistence of self-immolations a testament to Chinese authorities' policy failures in the region. "They are the ones that can do something about this, but they are powerless right now," said Tenzin Chokey, general secretary of the Tibetan Youth Congress in Dharamsala. "All their usual tactics have failed."