Water levels have plunged in a major river in India's northeast that originates in Tibet, local officials told AFP on Thursday, triggering speculation that China might be responsible.

The Brahmaputra has its source in China's southwestern Tibet region where it is known as the Yarlung Tsangpo, and it enters India in the mountainous, remote northeastern state of Arunachal Pradesh, where it it is called the Siang.

The 1,800-mile (2,900 kilometre) river then descends into the plains of adjoining Assam state and ends in Bangladesh in the Bay of Bengal, along the way supplying water to hundreds of millions of farmers and residents.

"It was shocking to find the Siang river drying up and patches of sand visible on its bed in a very large stretch close to Pasighat town," local state lawmaker Tako Dabi told AFP by telephone from the scene.

"We suspect the sudden drying up of the Siang could be a result of China either diverting the river water on their side or due to some artificial blockades somewhere in the upper reaches," added Dabi, an advisor to the state's chief minister and a former home minister.

He estimated the flow was about 40 percent of its normal strength.

"The water level has reduced by roughly three meters (10 feet) in the past few days and we really don't know the reason," K. Apung, an engineer at the State Water Resources Department in Pasighat, explained to AFP.

Video footage from the scene showed the Siang -- normally a gushing torrent several kilometres (miles) wide at Pasighat, according to Dabi -- reduced to flowing in narrow channels in a large sandy riverbed.

The problem was highlighted on the day the Chinese Foreign Minister Yang Jiechi held talks in New Delhi with his Indian counterpart S.M. Krishna.

India is extremely nervous about the danger of its giant northern neighbour diverting rivers that originate in Tibet and flow into India, or disrupting their flow with hydroelectric plants.

The two countries have held frequent talks about the issue at the highest level.

"We have been assured that nothing will be done which affects India's interests adversely," Indian Premier Manmohan Singh told the upper house of parliament last August.

Energy-hungry and water-deficient China is building hydroelectric facilities on the Yarlung Tsangpo. India says it has received assurances they are "run-of-the-river" projects rather than dams which would disrupt the flow.

"Our satellite pictures convey that no such activity of any storage facility is being worked out by the Chinese authorities," Krishna told reporters on Thursday after his talks with his Chinese counterpart.

He said that in light of the media reports about the river's flow, "we will get our ambassador (in Beijing) to check it."

A senior official at the water resources ministry in New Delhi, who asked not to be named, denied that there was any problem.

"The river drying up is a figment of their imagination," he told AFP.

Brahma Chellaney, an expert in New Delhi who has written extensively on water issues in Asia, said the alarm in Arunachal warranted further investigation.

He said China had not signed any water-sharing agreements in accordance with international norms with its many downstream neighbours who are dependent on the vast fresh water flows from the Tibetan plateau.

"If you look at the pattern, they (China) build dams and initiate them very quietly," Chellaney told AFP, citing the experience of countries downstream on the Mekong river.

India and China have decided that 2012 will be the "India-China year of Friendship and Cooperation" in a bid to overcome mutual mistrust and suspicion that continues to bedevil their relations.

The two Asian giants have an unresolved border dispute that was the cause of a brief but bloody war in 1962.

China claims almost all of Arunachal Pradesh as its own territory.