People are building barriers in some parts of Pakistan on Thursday to hold back rising waters that have engulfed nearly a third of the country after weeks of rain, while officials said 12 more deaths took the toll to 1,355.

Hundreds of thousands have been forced from their homes in a disaster blamed on climate change estimated to have caused losses of about $10 billion, disrupting the lives of nearly 33 million of a population of 220 million.

People worked to strengthen an existing dyke as floodwaters threatened the town of Bhan Syedabad in the southern province of Sindh, one of the worst-hit regions.

A short distance away, Pakistan's largest freshwater lake of Manchar is dangerously close to bursting its banks, as high water levels persist despite breaches by authorities to stave off further floods in an effort that displaced 100,000 people.

National disaster authorities said 12 deaths in the last 24 hours carried the toll to 1,355. Seven were children, who make up 481 of the dead.

The floods were brought by record monsoon rains and glacier melt in the northern mountains. In July and August, Pakistan received 391 millimeters (15.4 inches) of rain, or nearly 190% more than the 30-year average, while Sindh got 466% more than the average.

The World Health Organization has said more than 6.4 million people need humanitarian support in the flooded areas. The United Nations has called for $160 million in aid.

The government has boosted cash handouts to flood victims to 70 billion Pakistani rupees ($314 million) and will buy 200,000 tents to house displaced families, authorities have said.

In televised remarks, Prime Minister Shahbaz Sharif said Wednesday he visited Sindh earlier in the day and saw what he described as something resembling "a sea of water" in the province - adding that he had never seen such devastation in his life before.