Family members sit on a charpoy (rope bed) as they flee a flooded village in Pakistan's Muzaffargarh district of Punjab province on Sunday. (Asim Tanveer/Reuters)

Muslim countries, organizations and individuals have pledged nearly $1 billion US in cash and relief supplies to help Pakistan respond to the worst floods in the nation's history, the head of a group of Islamic states said Sunday.

The announcement came as floodwaters inundated a large town in Pakistan and authorities struggled to build new levees with clay and stone to prevent one of the area's biggest cities from suffering the same fate.

Countries have pledged hundreds of millions of dollars to help Pakistan cope with the floods, which first struck about a month ago after extremely heavy monsoon rains. But some officials had criticized the Muslim world for not contributing enough.

Ekmeleddin Ihsanoglu, head of the 57-member Organization of the Islamic Conference, likely sought to counter that criticism by announcing that Muslims have pledged nearly $1 billion. The pledges came from Muslim states, non-government organizations, OIC institutions and telethons held in Saudi Arabia, Turkey, Kuwait, the United Arab Emirates and Qatar, he said.

"They have shown that they are one of the largest contributors of assistance both in kind and cash," said Ihsanoglu of the various donors. He spoke during a joint news conference with Pakistani Foreign Minister Shah Mahmood Qureshi in Islamabad.

Ihsanoglu did not provide a breakdown of the pledges or say how much of the money would flow through the Pakistani government versus independent organizations.

Pakistani Prime Minister Yousuf Raza Gilani on Sunday criticized donations made to foreign NGOs rather than the Pakistani government, saying much of the money would be wasted.

"Eighty per cent of the aid will not come to you directly," said Gilani, referring to Pakistani citizens.

"It will come through their NGOs, and they will eat half of it," he said during a news conference in his hometown of Multan.

The floods began in the mountainous northwest about a month ago and have moved slowly down the country toward the coast in the south, inundating vast swaths of prime agricultural land and damaging or destroying more than one million homes.

Latest flooding

Floodwaters surged into the southern town of Sujawal on Sunday after breaking through a levee on the Indus River two days earlier, said Hadi Baksh, a disaster management official in southern Sindh province. Most of the town's 250,000 residents had already fled, but the damage to homes, clinics and schools added to the widespread devastation the floods have caused across Pakistan.

Authorities in Sujawal were trying to limit the flood damage, but the water level has already risen up to 1.5 metres in the centre of town and three metres in the surrounding villages, said Anwarul Haq, the top official in Sujawal.

The floodwaters also threatened Thatta, a historic city of some 350,000 people who have mostly fled to higher ground. Thatta is the base of operations for local authorities trying to cope with a disaster that has overwhelmed the Pakistani government and international partners who have stepped in to help.

Authorities rushed to build makeshift levees across the road connecting Sujawal and Thatta, parts of which were already flooded, Baksh said.

"We are trying to plug the bridges at three different points to stop the water flow toward Thatta," said Baksh. "We are trying all our best efforts."

Thatta is located about 125 kilometres southeast of the major coastal city of Karachi and 25 kilometres northwest of Sujawal. Many of the people who fled Sujawal and Thatta headed to Makli, a hill just south of Thatta that contains a vast Muslim graveyard.

About half a million flood victims are camped out on the hill, Baksh said. Most lack any form of shelter and are desperate for food and water.

"We don't have water to drink, not to mention food, tents or any other facility," said Mohammed Usman, a labourer who fled Sujawal several days ago and needed water to help cope with a painful kidney stone.

The United Nations, the Pakistani army and a host of local and international relief groups have rushed aid workers, medicine, food and water to the affected regions, but are unable to reach many of the eight million people who are in need of emergency assistance.

The U.S. said Saturday it would deploy an additional 18 helicopters to help with the relief effort. The U.S. military is already operating 15 helicopters and three C-130 aircraft in the country, the U.S. Embassy said in a statement.