Waters have exceeded the danger level at a key flood barrier in Pakistan's southern province of Sindh.
It means Sindh faces as much devastation as in the badly hit parts of northwestern Pakistan, the BBC reports.
Monsoon rains show little sign of abating, which is expected to compound the misery of more than 13 million people - about 8% of the population - whose lives have been disrupted by the flooding.
At least 1600 people have died in the region's worst flood in decades.
Survivors, angry at the pace of the relief effort, have been attacking government officials in flood-hit areas.
Soldiers and aid workers are struggling to reach at least a million people cut off by landslides, and poor weather has grounded relief helicopters.