Pakistan's eastern towns of Chiniot and Hafizabad face a risk of catastrophic floods if an irrigation barrage crumbles on a major river upstream after heavy rains swelled it beyond capacity, officials warned on Thursday.

India and Pakistan are battling torrential monsoon rains that have unleashed flash floods, swelled rivers and filled dams, with 60 deaths in Indian Kashmir in July and 805 in Pakistan since late June.

Any flooding blamed on India stands to inflame relations between the arch-foes, embroiled in a tense stand-off since a brief conflict in May that was their worst fighting in decades.

The waters of the Chenab river in Pakistan's sprawling province of Punjab threatened to burst through a 1,000-metre concrete barrage at Qadirabad that regulates flows, siphoning them into a canal irrigation network.

"It is a crisis situation," said a technical expert at the National Disaster Management Authority, adding that the collapse of the barrage could wash away the towns, home to more than 2.8 million.

"Under the constant supervision of experts and administration, the water level is receding, but it is still not beyond danger levels," added the official.

More than one million people have been evacuated from Punjab province due to flooding caused by heavy rain, the provincial disaster authority said.

The threat comes as India's release of excess water this week from its dams swelled river flows downstream in Punjab, home to half the population of 240 million.

India routinely releases water from its dams when they get too full, with the excess flowing into Pakistan, accompanied by warnings from New Delhi, which calls them a humanitarian measure.

On Thursday, Pakistani officials said India passed on its third flood warning since Sunday, this time for the Sutlej, while the previous two concerned waters heading into Pakistan on the Ravi.

India's water resources ministry did not immediately respond to a Reuters request for comment on the matter.

More than 900,000 cusec of water passed through the Qadirabad distribution structure on the Chenab river, or 100,000 cusec in excess of its capacity, the provincial disaster management authority said. A cusec is a flow of volume equivalent to one cubic foot, or 28 cubic litres, every second. (Reuters)