People in Sindh province blocked a highway to protest the slowness of aid delivery and clashed with police, the United Nations said. In a hard-hit district of Punjab, hungry mobs unloaded two aid trucks headed to a warehouse. Local aid agencies reported other incidents of looting.

An aid agency worker said distributions were hampered because of the crowds stopping the convoys and because large numbers of people were living along the road.

About 20 million people have been affected by the relentless monsoon rains that began falling three weeks ago, leading to massive flooding from the mountainous regions in the north to the river plains of the south.

About one-fifth of Pakistan is submerged, and entire families waded through filthy water, pleading for help.

More than 1,400 people have died. Health officials fear a second wave of fatalities from waterborne diseases, including cholera, which is endemic in Pakistan and now threatening to become a major outbreak.

Up to 3.5 million children are at high risk of cholera and other deadly diseases such as typhoid and dysentery, said Maurizio Giuliano of the United Nations' humanitarian affairs office. About 900,000 homes have been damaged, and the monsoon season is only about halfway over.

Water is the villain here but can also be a savior: The only recourses from waterborne illnesses are clean water and medical care, but both are in short supply.

The United Nations has called for US$166 million for clean water and medical care but has received only US$25 million.

The World Bank has committed about US$900 million at the request of the Pakistani government. According to a statement, funding will come from the bank's Fund for the Poorest through reprogramming of currently planned projects and reallocation of undisbursed funds from ongoing projects.

The overall global response has not been nearly enough, according to an International Rescue Committee-chaired consortium, the Pakistan Humanitarian Forum.

About US$150 million had been received from nations around the world by Monday, the group said in a statement, but much more is needed.