Ireland is sending its largest ever shipment of humanitarian aid to flood-stricken Pakistan.

The shipment, comprising 98 tonnes of equipment, including shelters and water, will be airlifted into the country by jet over the coming days and distributed to the Irish aid agencies Concern, Trócaire, Goal and Plan Ireland.

The consignment is large enough to provide supplies for up to 33,000 people.

Minister of State for Overseas Development Peter Power said the aid was badly needed.

Meanwhile, the United Nations has warned that tens of thousands of children risk death from malnutrition as flood waters threaten to engulf two towns in southern Pakistan a month after the disaster began.

The floods are Pakistan's worst-ever natural disaster in terms of the amount of damage and the number of people affected, with more than six million people forced from their homes, about a million of them in the last few days as the water flows south.

The disaster has killed about 1,600 people, inflicted billions of dollars of damage to homes, infrastructure and the vital agriculture sector and stirred anger against the government which has struggled to cope.

Floodwaters are beginning to recede across most of the country as the water flows downstream, but high tides in the Arabian Sea mean they still pose a threat to towns in Sindh province such as Thatta, 70km east of Karachi.

Water broke the banks of the Indus near Thatta and also broke out of a feeder canal running off the river, compounding the danger, Riaz Ahmed Soomro, relief commissioner in the southern province of Sindh, told Reuters.

Tens of thousands of people have poured out of the delta town, which normally has a population of about 300,000, after authorities told people to leave.

The floods began in late July after torrential monsoon downpours over the upper Indus basin.

The floods have damaged at least 3.2 million hectares - about 14% of Pakistan's entire cultivated land - according to the United Nation's food agency.

The total cost in crop damages is believed to be about $2.86 billion (€2.25bn).

Authorities have been battling for days to save the town of Shahdadkot in northern Sindh's rice-growing belt, raising an embankment several kilometres long as the water has crept higher.

The United Nations said aid workers were becoming increasingly worried about disease and hunger, especially among children in areas where even before the disaster, acute malnutrition was high.