Millions of Pakistanis remain dependent on aid handouts after the country's worst flooding in history [EPA]

Pakistani authorities are racing to protect two southern towns and their 360,000 residents from surging floods, as the nation struggles to cope with its worst natural disaster in nearly a century.

Advancing floodwaters continue to threaten towns in Sindh province, where 19 of its 23 districts have been deluged, displacing more than 2.8 million people, according to provincial authorities.

"The situation is a bit serious in Johi town and Dadu. We are  taking all-out measures to save them from ravaging floodwaters,"  provincial irrigation minister Jam Saifullah Dharejo told AFP news agency on Monday.

"The water is 20km away from Dadu city but we cannot  rule out a serious threat to this city," one of the largest in the  north of Sindh, Dharejo said.

"We are making all our efforts to save Dadu and Johi," he  added.

Dadu and Johi are about 320km north of the  main southern port city of Karachi and officials fear the waters will breach protective embankments unless they are quickly strengthened.

District coordination officer Iqbal Memon said Johi was most in danger of the advancing floods.

"The floodwaters are fast heading towards Johi town after inundating most parts of Khairpur Nathan Shah and Mehar towns and several surrounding villages in Dadu district," he said.

"For two days, we are employing all available means to strengthen the protective embankments around Dadu and Johi but the threat still remains," he said.

About 80 per cent of the Johi's population of 60,000 had already fled to safer areas.

Meanwhile, troops had evacuated 2,644 people from flood-hit areas of Jati, Mehar, Johi, Shahdad Kot and Sujawal, the military said in a statement.

Milions aid dependent

"Army has established 25 relief camps in Sindh," it said, adding that 33,047 people were given cooked food during the previous 24 hours.

A month and a half after monsoons caused devastating floods throughout the country, submerging an area the size of England, eight million people remain dependent on handouts for their survival, which many say are too slow coming.

The UN has warned that the slow pace of aid pledges could impede relief operations and says Pakistan faces a triple threat to food supplies - with seeds, crops and incomes hit.

The floods have ruined 3.6 million hectares (8.9 million acres) of rich farmland, and the UN's Food and Agriculture Organisation said farmers urgently needed seeds to plant for next year's crops.

Prime minister Yousuf Raza Gilani has warned that the country faces inflation of up to 20 per cent and slower growth because of the disaster.

The floods have killed 1,760 people but disaster officials have said the number of deaths is likely to rise "significantly" when the missing are accounted for.

Source: Agencies