Thousands of Pakistanis are fleeing their homes in southern coastal areas as floods sweep down from the north, reports BBC News.
Some 200,000 people have been evacuated in the Thatta area of Sindh province, where dozens of villages are submerged.
In the north, workers have begun clearing up as the floods recede. The UN has appealed for more helicopters to reach 800,000 people who are cut off.
Doctors in many areas are struggling to cope with the spread of water-borne diseases such as diarrhoea and cholera.
Five million Pakistanis have no shelter, and urgently need tents or plastic sheeting to protect them from the sun.
The UN says more than 17 million people have been affected by the monsoon floods, and about 1.2 million homes have been destroyed.
The vast body of flood-water that has swept the length of Pakistan is now threatening previously unaffected communities in Sindh province, at the country’s southern tip.
The authorities have been organising a mass evacuation from the town of Thatta – near the mouth of the Indus delta – and surrounding villages.
At the moment, all that stands between locals and the vast weight of water is an embankment which has started to crack in places. If it bursts, the whole area could be submerged.
“We are very vigilant, we are watching and we are strengthening wherever we see any weakness on these protection walls,” Manzoor Ali Sheikh, a senior local official in Thatta told the BBC.
“We are hopeful that they will not give way to the water and water will pass through these bunds (embankments) to the sea.”
Elsewhere in Sindh people are still battling to hold back the flood-waters.