KOT ADDU, Pakistan -- Floodwaters ravaged hundreds of villages in Pakistan's heartland Wednesday, killing dozens more people and destroying thousands of homes.

Aid workers warned that bloated rivers would soon surge into the country's south, and said Pakistanis should prepare for more evacuations.

This year's monsoon season has prompted the worst flooding in Pakistan in living memory, and already killed more than 1,500 people. The UN scrambled to provide food and other assistance to some 3.2 million people affected in the water-soaked nation, which was already struggling with an Islamist militancy and a poor economy.

In Pakistan's Punjab province, floodwaters deluged numerous villages and began pouring into major urban centers such as the city of Kot Addu. The army used boats and helicopters to move stranded villagers in the area to higher ground.

Water levels were so high in large tracts of Kot Addu and the nearby area of Layyah in the south of the province, that only treetops and uppermost floors of some buildings were visible.

Military spokesman Major General Nadir Zeb told reporters Wednesday that at least 30,000 people have been rescued from flood-hit zones in Kot Addu and nearby areas over the previous 72 hours. He warned that more flooding was expected as weather forecasts predicted more rains in the next few days.

"People must cooperate with us, and they must leave those areas where floods are going to hit," he said.

At least 47 people had been killed in Punjab, Pakistan's National Disaster Management Authority said. Nearly 1,000 villages have been affected and some 15,000 houses destroyed in the province, UN officials said.

The rush of muddy water over river banks in Punjab threatened to destroy vast stretches of crops that make the province Pakistan's breadbasket. Numerous crops have also been lost in the northwest, the hardest hit region.

The loss of farm produce is one reason the UN has warned of serious food shortages, and the World Food Program has estimated that 1.8 million people will need to be fed over the next month.

Rescue workers have struggled to deliver aid because of washed-out bridges and roads and downed communication lines.

Several foreign countries have stepped in to help, including the United States, which announced Tuesday that it was sending six large military helicopters from Afghanistan to help with the relief effort.

But many flood victims have complained that aid is not reaching them fast enough or at all. That anger could spread as floodwaters threaten Sindh province in Pakistan's south.

Authorities expect several districts will be hit by rising waters in Sindh, which is on track to experience its worst flooding in 34 years, the UN said. (AP)