Thousands of people have been detained in Indian Kashmir over fears of outbreaks of unrest after New Delhi stripped the restive region of its autonomy two weeks ago, government sources told AFP.

A magistrate speaking to AFP on condition of anonymity said at least 4,000 people were arrested and held under the Public Safety Act (PSA), a controversial law that allows authorities to imprison someone for up to two years without charge or trial.

"Most of them were flown out of Kashmir because prisons here have run out of capacity," the magistrate said, adding that he had used a satellite phone allocated to him to collate the figures from colleagues across the Himalayan territory amid a communications blackout imposed by authorities.

Authorities have repeatedly declined to provide a tally of how many people have been taken into custody, apart from confirming more than 100 local politicians, activists and academics were detained in the first few days after the state was stripped of its semi-autonomous status.

They said the "few preventive detentions" were made to avoid a "breach of the peace" in a region that has fought an armed rebellion against Indian rule for three decades.

Jammu and Kashmir government spokesman Rohit Kansal said previously there was "no centralised figure" for the total number of people detained.

But AFP spoke to numerous government officials in Kashmir's main city of Srinagar, including police and security personnel, who confirmed the sweeping arrests.

A police official who asked to remain anonymous told AFP "around 6,000 people were medically examined at a couple of places in Srinagar after they were detained".

"They are first sent to the central jail in Srinagar and later flown out of here in military aircrafts," he added.

Another security official said "thousands are jailed" but that the figure did not include other residents whose detentions at police stations had not been recorded.

The revelations came as eight people were injured during weekend protests in Srinagar with authorities reimposing heavy restrictions to quell any unrest.

Authorities were gradually easing a massive movement and communications lockdown imposed two weeks ago.

But clashes in a dozen locations around Srinagar on Saturday saw restrictions brought back in some locations, the Press Trust of India news agency reported, citing unnamed officials.

Authorities have previously denied or played down reports of any violence and stressed that most of the Muslim-majority Kashmir Valley has been peaceful.

State government spokesman Kansal told reporters late Saturday that eight people had been injured in the clashes but did not provide further details.

A senior government official told AFP earlier Sunday that more telephone exchanges would return to normal operations "by the evening".

Schools in some areas would reopen on Monday, officials said.

In the Hindu-majority city of Jammu, authorities cut mobile internet services on Sunday and warned locals not to circulate messages or videos on social media that they said were fake, PTI reported.

New Delhi's shock decision has sparked public anger and frustration and there have been several rallies in Srinagar attracting thousands of demonstrators.