Mehbooba Mufti and Omar Abdullah, former chief ministers of Indian-occupied Kashmir, along with two other prominent political leaders were arrested on Monday, Press Trust of India reported.
"J&K People’s Conference leaders Sajjad Lone and Imran Ansari were also arrested," a Hindustan Times report said, citing officials.
According to a notice issued to Mufti, the Jammu and Kashmir People’s Democratic Party chief, she has been detained because her activities “are likely to cause breach of peace”.
The arrests come hours after the Bharatiya Janata Party-led Indian government scrapped Article 370 of the Indian constitution which granted special status to IoK.
The article gave Kashmir its own constitution and decision-making rights for all matters except for defence, communications and foreign affairs.
The law also forbade Indians outside the state from permanently settling, buying land, holding local government jobs and securing education scholarships.
Critics of India's Hindu nationalist-led government see the move as a bid to dilute the demographics of Muslim-majority Kashmir with Hindu settlers.
'Today marks the darkest day in Indian democracy'
Earlier in the day, Mufti and Abdullah had condemned BJP's revocation of the special constitutional status of occupied Kashmir.
"Today marks the darkest day in Indian democracy. Decision of Jammu and Kashmir leadership to reject two nation theory in 1947 & align with India has backfired. Unilateral decision of Government of India to scrap Article 370 is illegal & unconstitutional which will make India an occupational force in J&K," Mufti said in the first of many tweets.
"It will have catastrophic consequences for the subcontinent. Government of India's intentions are clear. They want the territory of J&K by terrorising it’s people. India has failed Kashmir in keeping its promises.
"Already under house arrest & not allowed to have visitors either. Not sure how long I’ll be able to communicate. Is this the India we acceded to?
"GOIs intention is clear & sinister. They want to change demography of the only Muslim majority state in India, disempower Muslims to the extent where they become second class citizens in their own state.
"The way some sections of media & civil society are celebrating these developments with glee is disgusting & disconcerting."
'A long and tough battle lies ahead'
Omar Abdullah, vice-president of National Conference and former chief minister of Jammu & Kashmir, also issued a statement.
"Government of India's unilateral and shocking decisions today are a total betrayal of the trust that the people of Jammu & Kashmir had reposed in India when the State acceded to it in 1947 — the decisions will have far-reaching and dangerous consequences.
"This is an aggression against people of the State as had been warned by an all-parties meeting in Srinagar yesterday.
"GOI has resorted to deceit and stealth in recent weeks to lay the ground for these disastrous decisions. Our darkest apprehensions have unfortunately come true after the GOI and it's representatives in Jammu and Kashmir lied to us that nothing major was planned.
"The announcement was made after the entire State, particularly the Kashmir Valley, was turned into a garrison. Those of us who gave democratic voice to the people of Jammu & Kashmir, are incarcerated as thousands of armed security personnel have been put on the ground.
"The scrapping of Articles 370 and 35A raise fundamental questions on the state's accession because that was done on the very terms enunciated in these Articles.
"The decisions are unilateral, illegal and unconstitutional and will be challenged as such by the National Conference . A long and tough battle lies ahead. We are ready for that."
Regional parties in occupied Kashmir have been calling attempts to revoke Article 370 an aggression against the people.
The law dates to 1927, when an order by the administration of the-then princely state of Kashmir gave the state's subjects exclusive hereditary rights. Two months after India won independence from British rule in August 1947, Maharaja Hari Singh, the ruler of Kashmir, signed a Treaty of Accession for the state to join the rest of the union, formalised in Article 370 of the Indian constitution. Further discussions culminated in the 1952 Delhi Agreement, a presidential order that extended Indian citizenship to the residents of the state but left the maharaja's privileges for residents intact.
Late Sunday in Kashmir, government forces laid steel barricades and razor wire on roads and intersections to cut off neighborhoods in Srinagar. The government issued a security order banning public meetings, rallies and movement and said schools would be closed.
Authorities also suspended internet services on cellphones, a common tactic to prevent anti-India demonstrations from being organised and to stop the dissemination of news.
Today's measure will impact about 7 million people living in the region.
The security deployment in recent days adds at least 10,000 soldiers and other forces in Kashmir, to what was already one of the world's most militarised regions.
India had also ordered thousands of tourists and Hindu pilgrims to leave the region.