Chinese authorities have begun constructing what will be the world's largest hydropower dam in Tibetan territory, in a project that has sparked concerns from India and Bangladesh.

Chinese Premier Li Qiang presided over a ceremony marking the start of construction on the Yarlung Tsangpo river on Saturday, according to local media.

The river flows through the Tibetan plateau. The project has attracted criticism for its potential impact on millions of Indians and Bangladeshis living downriver, as well as the surrounding environment and local Tibetans.

Beijing says the scheme, costing an estimated 1.2tn yuan ($167bn; £125bn), will prioritise ecological protection and boost local prosperity.

When completed, the project - also known as the Motuo Hydropower Station - will overtake the Three Gorges dam as the world's largest, and could generate three times more energy.

Experts and officials have flagged concerns that the new dam would empower China to control or divert the trans-border Yarlung Tsangpo, which flows south into India's Arunachal Pradesh and Assam states as well as Bangladesh, where it feeds into the Siang, Brahmaputra and Jamuna rivers.

A 2020 report published by the Lowy Institute, an Australian-based think tank, noted that "control over these rivers [in the Tibetan Plateau] effectively gives China a chokehold on India's economy".

In an interview with news agency PTI earlier this month, Arunachal Pradesh chief minister Pema Khandu expressed concern that the Siang and Brahmaputra could "dry up considerably" once the dam was completed.

He added that the dam was "going to cause an existential threat to our tribes and our livelihoods. It is quite serious because China could even use this as a sort of 'water bomb'".

"Suppose the dam is built and they suddenly release water, our entire Siang belt would be destroyed," he said. "In particular, the Adi tribe and similar groups... would see all their property, land, and especially human life, suffer devastating effects."

In January a spokesperson for India's ministry of external affairs said they had expressed concerns to China about the impact of mega-dams and had urged Beijing to "ensure the interests of downstream states" were not harmed. They had also emphasised the "need for transparency and consultation with downstream countries".

India plans to build a hydropower dam on the Siang river, which would act as a buffer against sudden water releases from China's dam and prevent flooding in their areas.

China's foreign ministry has previously responded to India, saying in 2020 that China has a "legitimate right" to dam the river and has considered downstream impacts.

Bangladesh also expressed concerns to China about the project, with officials in February sending a letter to Beijing requesting more information on the dam.

Chinese authorities have long eyed the hydropower potential of the dam's location in the Tibet Autonomous Region.

It's in a massive canyon that is said to be the world's deepest and longest on land, along a section where the Yarlung Tsangpo - Tibet's longest river - makes a sharp U-turn around the Namcha Barwa mountain.

In the process of making this turn - which has been termed "the Great Bend" - the river drops hundreds of metres in its elevation.

Earlier reports indicated that authorities planned to drill multiple 20km-long tunnels through the Namcha Barwa mountain, via which they would divert part of the river.

Over the weekend a Xinhua report on Li Qiang's visit said that engineers would conduct "straightening" work and "divert water through tunnels" to build five cascading power stations.

Xinhua also reported that the hydropower dam's electricity would be mainly transmitted out of the region to be used elsewhere, while accommodating for Tibet's needs.

China has been eyeing the steep valleys and mighty rivers in the rural west - where Tibetan territories are located - to build mega-dams and hydropower stations that can sustain the country's electricity-hungry eastern metropolises. President Xi Jinping has personally pushed for this in a policy called "xidiandongsong", or "sending western electricity eastwards".

The Chinese government and state media have presented these dams as a win-win solution that cuts pollution and generates clean energy while uplifting rural Tibetans.

But activists say the dams are the latest example of Beijing's exploitation of Tibetans and their land - and past protests have been crushed.

Last year, the Chinese government rounded up hundreds of Tibetans who had been protesting against another hydropower dam. It ended in arrests and beatings, with some people seriously injured, the BBC learned through sources and verified footage.

There are also environmental concerns over the flooding of Tibetan valleys renowned for their biodiversity, and the possible dangers of building dams in a region rife with earthquake fault lines.

CORRECTION 21 July 2025: An earlier version of this story incorrectly stated that the estimated cost of the dam was $1.67bn.