Pakistan's armed forces have rescued a further 2,000 people stranded by rising floodwaters, they said on Friday, in a disaster blamed on climate change that has swamped about a third of the south Asian nation and is still growing.

Record monsoon rains and melting glaciers in northern mountains brought floods that have killed at least 1,208 people, including 416 children, the National Disaster Management Authority (NDMA) has said.

The United Nations has appealed for $160 million in aid to help tackle what it said was an "unprecedented climate catastrophe" as Pakistan's navy has fanned out inland to carry out relief operations in areas that resemble a sea.

"During the last 24 hours, 1,991 stranded individuals have been evacuated," the armed forces said in a statement, adding that nearly 163 tonnes of relief supplies had also been delivered to the flood-affected.

On Thursday, the military said it had evacuated about 50,000 people, including 1,000 by air, since rescue efforts began.

Several humanitarian relief flights are set to arrive on Friday from Middle Eastern nations such as Qatar and the United Arab Emirates, Pakistan's foreign office said.

Weather officials predict more rains and flash flooding in the month of September, with southern regions bracing for a surge of water from the Indus river.

Sindh, one of the worst-affected provinces, has asked relief camps to deploy additional female doctors and medical officers, to ensure adequate care as more pregnant women and young mothers are displaced by the waters.

The navy airlifted more than 150 people from villages in Sindh's district of Dadu on Thursday, it said in a statement.

Pakistan received nearly 190% more rain than its 30-year average in the quarter from June to August, totalling 390.7mm (15.38 inches).