Indian Prime Minister Narendra Modi's plan to change the status of Kashmir has run into fierce opposition from China and Pakistan as a communications blackout in the disputed territory entered a second day.

Moving to tighten its grip on India's only Muslim-majority region, the government dropped Article 370a from its constitution, which allows the states of Jammu and Kashmir to make its own laws. 

The changes imposed by Mr Modi's Hindu nationalist-led government are the most sweeping in the nearly 30 years that India has been battling a revolt in Kashmir.

The government also broke up the state into two federally administered territories.

China said it opposed India's decision to revoke Kashmir's special status and that India needed to be cautious on border issues.

"India's action is unacceptable and would not have any legal effect," Foreign Ministry spokeswoman Hua Chunying said in a statement, drawing an immediate rebuke from India that Kashmir was an internal affair.

The Himalayan region is divided between India, which rules the populous Kashmir Valley and the Hindu-dominated region around Jammu city, Pakistan, which controls a wedge of territory in the west, and China, which holds a thinly populated high-altitude area in the north.

China urged India to strictly abide by the agreements reached by both countries in order to avoid any actions that would further complicate boundary issues, Ms Hua said.

India and China have a long-standing dispute over the border, including in Ladakh, the high altitude area.

Indian foreign ministry spokesman Raveesh Kumar said splitting Jammu and Kashmir into federal territories was a domestic issue.

"India does not comment on the internal affairs of other countries and similarly expects other countries to do likewise," he said.

Thousands of paramilitary troops have been deployed in Kashmir and phone and internet services have been suspended, prompting criticism the government is trying to stifle all dissent.

Video images by Reuters partner ANI showed deserted streets in Srinagar, the main city of the region at the heart of the decades-long armed revolt, which India accuses Pakistan of helping.

Pakistan says it gives only moral and diplomatic support to the Kashmiri people in their struggle for self-determination.

After a meeting with top commanders in the city of Rawalpindi, Pakistan's army chief expressed support for the people of Kashmir, and the prime minister said he was weighing an approach to the United Nations Security Council.

"The Pakistan Army firmly stands by the Kashmiris in their just struggle to the very end," said General Qamar Javed Bajwa.

"We are prepared and shall go to any extent to fulfil our obligations in this regard."

The nuclear-armed neighbours have fought two of their three wars over the territory, and engaged in an aerial clash in February after a militant group based in Pakistan claimed responsibility for an attack on an Indian military convoy.

"We will fight it (Mr Modi's policy) at every forum. We're thinking how we can take it to International Court (of Justice) ... to the United Nations Security Council," Prime Minister Imran Khan told Pakistan's parliament.