Pakistan's government hit back on Thursday with a string of tit-for-tat measures against its neighbour India, who accused Islamabad of supporting "cross-border terrorism" following a brutal attack on Indian tourists.

Prime Minister Shehbaz Sharif convened a rare meeting of the National Security Committee (NSC) with top military officials, including powerful Chief of Army Staff Asim Munir, in the capital Islamabad in response to India's measures.

"Any threat to Pakistan's sovereignty and to the security of its people will be met with firm reciprocal measures in all domains," a statement released by Prime Minister Shehbaz Sharif's office said after the NSC meeting.

New Delhi suspended a water-sharing treaty, announced the closure of the main land border crossing with Pakistan, downgraded diplomatic ties and withdrew visas for Pakistanis on Wednesday night, just over 24 hours after gunmen killed 26 men in Indian-administered Kashmir.

The slew of measures announced by the Pakistan government in response on Thursday included expelling Indian diplomats and cancelling visas for Indian nationals with the exception of Sikh pilgrims.

Pakistan also warned that it would consider any attempt by India to stop the supply of water from the Indus River an "act of war and responded with full force across the complete spectrum of national power".

Islamabad said Indian military advisers were "persona non grata".

"They are directed to leave Pakistan immediately," the statement said.

Pakistan's airspace was also closed with immediate effect "for all Indian owned or Indian operated airlines", while the main Wagah border crossing in Punjab was also closed.

"All cross-border transit from India through this route shall be suspended, without exception," the statement said.

"All trade with India including to and from any third country through Pakistan is suspended forthwith."