Tens of thousands of people in southern Pakistan are fleeing a threatened flood-surge, three weeks after heavy monsoon rains first hit the country.
In the city of Shahdadkot, a hastily built barrier has been breached, allowing floodwaters to approach.
An estimated 4 million people have now been displaced in the city of Sukkar alone.
Meanwhile, the World Health Organization (WHO) says diseases are spreading in affected areas.
Sindh in the south is now being described as the country's worst-hit province, with officials saying at least 200,000 residents have fled in the last 24 hours.
'Laden carts'
In Shahdadkot, the BBC's Jill McGivering says residents are leaving en masse to try to reach safe ground.
The makeshift 4ft mud barrier, built by the army and volunteers, was the city's last line of defence and has now been breached in several places.
Jam Saifullah Dharejo, Sindh provincial irrigation minister, said that most people had been escorted to safety, but efforts were under way to help those still stranded.
"We are trying to save the city from the unprecedented flood," he said.
Some residents say they do not want to leave.
"This is the place where I earn my bread and butter. I live here and will die here," Mohammad Jaffar, a shopkeeper, told Reuters news agency.
Mr Dharejo added that the floods did not pose a risk to Hyderabad, the province's second largest city.
Our correspondent says that, in Sukkar, a fraction of people are in relief camps - but the vast majority are out in the open, fending for themselves.
The WHO says displaced communities are highly vulnerable to epidemics because of a lack of sanitation and hygiene.
The organisation in its latest report said that over 200,000 people have reported acute diarrhoea, with about the same number suffering acute respiratory problems.
Millions of livestock are also at risk, according to the UN's Food and Agriculture Organisation (FAO), which said that at least 200,000 animals had died already as a result of the disaster.
The floods, which began last month in Pakistan's north-west and have since swept south, have killed at least 1,600 people and affected about 20 million.
Earlier, the International Monetary Fund said Pakistan faced a "massive economic challenge".
It is due to begin talks with Pakistani officials in Washington on Monday and said it would help Pakistan review the country's budget and financial prospects.
