Indian security forces have arrested more than 500 people since New Delhi imposed a communications blackout and security clampdown in divided Kashmir, where people remain holed up in their homes for a fourth day.

Pakistan, which claims the divided Himalayan region together with India, on Thursday suspended a key train service with India over a change in Kashmir's special status by New Delhi, as tensions between the rivals soared.

India's government this week revoked the special status of Jammu and Kashmir and downgraded the Himalayan region from statehood to a territory. Muslim-majority Kashmir is claimed in full by both India and Pakistan, and rebels have been fighting Indian rule in the portion it administers for decades.

State-run All India Radio, which reported on the arrests without details, also said cross-border firing by Indian and Pakistani troops in the Rajouri sector of India-run Kashmir late Wednesday.

In a nationally broadcast speech Thursday, Prime Minister Narendra Modi described the changes imposed by his government as historic and assured residents that the situation will soon become normal.

Modi said the "mainstreaming" of the Kashmiri people with the rest of the nation would expedite development and create new jobs with investment from public and private companies.

People watch as Prime Minister Narendra Modi delivers an address to the nation, on a TV screen in Ahmedabad, India Thursday. (Amit Dave/Reuters)

He accused neighbouring Pakistan of using the past arrangement "as a weapon to incite people of the region against India."

"I have complete faith under this new system we all will be able to free Jammu and Kashmir of terrorism and separatism," Modi said, referring to ending the region's special status granted under Articles 370 and 35A of India's constitution.

Those provisions "gave Jammu and Kashmir nothing but terrorism, separatism, dynasticism and large-scale spread of corruption," and they were "used as a weapon by Pakistan to incite anti-national feelings against some people in our country," he said.

Modi added: "This heaven on earth, our Jammu and Kashmir, will once again reach new heights of development and attract the whole world toward it. Ease of living will increase for our citizens. Citizens will receive all the benefits they deserve without any obstacles or challenges."

Watch as India-run Kashmir remains under tight security:

The streets in the city of Srinagar were largely deserted amid an ongoing security clampdown and communications blackout in India-run Kashmir. 0:59

UN Secretary General Antonio Guterres is calling on India and Pakistan to refrain from taking any steps that would affect the status of Kashmir.

UN spokesperson Stephane Dujarric told reporters Thursday, "The position of the United Nations on this region is governed by the charter of the United Nations and applicable Security Council resolutions."

He said Guterres also notes the 1972 Simla agreement on bilateral relations between India and Pakistan "which states that the final status of Jammu and Kashmir is to be settled by peaceful means, in accordance with the charter of the United Nations."

Streets and shops deserted

Critics have assailed the turn as a power grab after Modi and his Bharatiya Janata Party recently secured a strong mandate in national elections.

Kashmir is India's only Muslim-majority state and most people there oppose Indian rule. The insurgency that began in 1989 and India's ensuing crackdown have killed more than 70,000 people.

The streets of Srinagar, the region's main city, are lined with deserted shops, now that steel barricades and razor wire are cutting off neighbourhoods, and the Indian government has closed schools and banned public meetings.

"There is no one in sight on the roads," said resident Mehraj Ahmed. "It doesn't look like a curfew; people are imprisoned in their own homes. I feel like the situation in Kashmir will get worse and this could continue for the next four to five months. I feel like Kashmir is on the verge of burning."

Activist Ali Mohammed told the New Delhi Television news channel that he has been organizing ambulances to carry sick poor people to hospitals in Srinagar, the main city in India's portion of Kashmir, as local residents can't even use phones to ask for medical help.

"It's hell," a patient told the television channel.

Global Affairs Canada has advised Canadians to avoid all travel to Kashmir and Jammu.

"Movement restrictions may be put in place without notice," an updated warning on Thursday advised.

<a href="https://twitter.com/hashtag/India?src=hash&ref_src=twsrc%5Etfw">#India</a>: The Government of India announced on August 5, 2019, constitutional changes that will affect the internal political status of Jammu and Kashmir. Monitor local news and follow the instructions of local authorities. <a href="https://t.co/cqqD4PRzaI">https://t.co/cqqD4PRzaI</a> —@TravelGoC

In New Delhi, Congress party activist Tehseen Poonawalla said he expected the Supreme Court to hear his petition on Thursday seeking immediate lifting of curfew and other restrictions, including blocking of phone lines, internet and news channels in Kashmir.

He also sought the immediate release of Kashmiri leaders who have been detained, including Omar Abdullah and Mehbooba Mufti.

Another Congress member, Ghulam Nabi Azad, said security forces prevented him from visiting the Indian-administered portion of Kashmir, causing him to return from its main airport after spending several hours there.

Azad said he flew to Srinagar on Thursday to assess the situation. Upon his return to New Delhi, he told reporters he was not allowed to meet party leaders in Kashmir.

Pakistan downgrades ties

In response to India's action, Pakistan on Wednesday said it would downgrade its diplomatic ties with India, expel the Indian ambassador and suspend bilateral trade. Prime Minister Imran Khan told Pakistan's National Security Committee that his government will use all diplomatic channels "to expose the brutal Indian racist regime" and human rights violations in Kashmir, the government's statement said.

India said it regretted Pakistan's steps, adding in a statement that "the intention behind these measures is obviously to present an alarming picture to the world of our bilateral ties."

Indian security forces personnel stand guard next to concertina wire laid across a road in Srinagar during the security clampdown in Indian-controlled Kashmir. (Danish Ismail/Reuters)

The External Affairs Ministry said it was not surprising that Pakistan has negatively perceived India's decision to end Kashmir's special status as Islamabad "has used such sentiments to justify its cross-border terrorism."'

India and Pakistan have fought two of their three wars since independence over control of Kashmir. The first war ended in 1948 with a United Nation-brokered cease-fire that left Kashmir divided and promised its people a UN-sponsored referendum on the region's future.

Modi, in his speech, accused Pakistan of using the past arrangement "as a weapon to incite people of the region against India," and said he has complete faith that the new system will be able to free Kashmir from terrorism and separatism.

Pakistan said it would ask the UN to pressure India to reverse its decision to downgrade the Indian-administered portion of Kashmir from a state to two separate territories. The region also lost its right to fly its own flag and make many of its own decisions.

The government in Islamabad also said it would give diplomatic, political and moral support to people living in Kashmir and their "right of self-determination."