In Islamabad, there was some deployment of riot police outside the diplomatic enclave as a precautionary measure. All members of the Indian High Commission were reported to be safe. Rallies were held across the four provinces - Balochistan, Khyber Pakhtunkhwa, Punjab, Sindh - and in Pakistan Occupied Kashmir - with slogans of 'Kashmir banega Pakistan'.
Pakistan President Arif Alvi said India's attempt to "change the statusa of Jammu and Kashmir is against the resolution of the UN Security Council and against the wishes of the people of Kashmir".
The Foreign Office, in an official statement, while condemning and rejecting India's announcement of abrogating Article 370 that granted special status to Jammu and Kashmir, said Islamabad will "exercise all possible options to counter it".
While India with scrapping of Article 370 sought to highlight that Kashmir is like any other state of India, the Pakistan Foreign Office harped on Kashmir being an "internationally recognized disputed territory".
"As party to this international dispute, Pakistan will exercise all possible options to counter the illegal steps," it said.
The Parliamentary Committee of Kashmir held a meeting on Kashmir at Parliament House, chaired by chairman Syed Fakhar Imam. All the opposition leaders spoke and condemned India's move on Kashmir.
Prime Minister Imran Khan, who earlier in the day went about his official duties, including inaugurating a greening drive, without any official reaction, dialled the leaders of Malaysia and Turkey in the evening.
During his telephone talk with his Malaysian counterpart Mahathir Mohamad and later with Turkish President Erdogan said that India's announcement on the status of Jammu and Kashmir was in clear violation of the United Nations Security Council (UNSC) resolutions.
He stressed that it would deteriorate the peace and security of the region, and further undermine relations between the two neighbours.
The Malaysian premier expressed concern over the situation in Indian Jammu and Kashmir, according to a statement by the Foreign Office.
Erdogan assured PM Imran Khan that Turkey, with regard to Kashmir, would continue supporting Pakistan, according to a statement.
In Rawalpindi, Pakistan army chief General Qamar Javed Bajwa summoned a Corps Commanders Conference on Tuesday to discuss the Kashmir situation and also on giving a "befitting response" to India in case of any misadventure from their side.
Pakistan President Arif Alvi has summoned a joint session of the Parliament on Tuesday, which is to be attended by the chiefs of the armed forces. The session, to be attended by Imran Khan, has been called at 11 am.
Foreign Minister Shah Mahmood Qureshi, said that India is playing a "dangerous game". "Today, India has once again revived and internationalised the Kashmir issue. This will not solve the problem, rather it will escalate it," he said in remarks to the media.
Qureshi said the entire international community needs to condemn the Indian move.
The Foreign Minister said the international organisations cannot stay silent on this matter. "The Kashmir issue has become even more dire with India's decision," Qureshi said.
Opposition leaders, including Pakistan Peoples Party leader Bilawal Bhutto Zardari and Leader of Opposition in the National Assembly Shehbaz Sharif, called for a joint session of Parliament.
Earlier, even as strong reactions were pouring in from across Pakistan, Imran Khan, donning a green cap, inaugurated the 'Plant for Pakistan' drive in Islamabad and asked every Pakistani to play their role in saving future generations.
Meanwhile, Pakistan Muslim League-Nawaz president Shehbaz Sharif, addressing a press conference in Lahore, said Pakistan should immediately call for an emergency meeting of the UN Security Council.
"This is a matter of Pakistan's national interest, all of Pakistan is united. The time has come for Pakistan's political and military leadership to take collective decisions," he said.
Sharif said the situation was also a test for US President Donald Trump to prove that his offer of mediation in Kashmir was not on account of some "personal agenda" but that he was serious about it.
"Otherwise we will be forced to believe that this was President Trump's gimmick to pull American troops out of Afghanistan," he said.
Minister for Human Rights Shireen Mazari said: "Kashmir is recognised as a disputed territory in UNSC resolutions. India cannot alter its status through its parliament."
Mazari said the International Court of Justice should be approached along with the UN Security Council and other international forums and human rights organisations.
"This is illegal annexation of a militarily-occupied territory and completely unacceptable."
In a Twitter post, former finance minister and Pakistan Tehreek-e-Insaaf leader Asad Umar said the Indian constitutional amendment was in violation of international resolutions as well as India's own Constitution.
"Is India still a constitutional democracy or is [it] now practically under Hindutva raj?" he asked.
PPP leader Sherry Rehman questioned where the international community was in response to the developments in Indian Kashmir.
PML-N leader Maryam Nawaz, the daughter of former Prime Minister Nawaz Sharif, said she will hold a rally in Sargodha on Tuesday dedicated to Kashmir.
At a press conference, Jamaat-i-Islami emir Sirajul Haq said India through its unilateral actions of today had violated the Simla agreement and the UN charter. He urged political parties to unite for the cause of Kashmir despite their political differences.
He also expressed the fear that this move by India could "propel the region into war".
The Prime Minister of Azad Jammu and Kashmir (AJK) or Pakistan Occupied Kashmir, Prime Minister Raja Farooq Haider said by repealing the special status to Indian Kashmir, New Delhi has lost its control over the territory in its entirety.
In a press conference in Islamabad, Haider said: "India has formally lost Kashmir today. We were never a part of India but today it has lost Ladakh, Jammu and the valley as well."
Haider urged the government to contact world leaders and forums to intervene and help resolve the Kashmir dispute.
( With inputs from IANS )