Flooding in Pakistan has killed more than 800 people in a week, a government official said Saturday as rescuers struggled to reach marooned victims and some evacuees showed signs of fever, diarrhea and other waterborne diseases.

The flooding caused by record-breaking rainfalls caused massive destruction in the past week, especially in the northwest province, where officials said it was the worst deluge since 1929.

The U.N. estimated Saturday that some 1 million people nationwide were affected by the disaster, though it didn't specify exactly what that meant.

The information minister for the northwest province, Mian Iftikhar Hussain, said reports coming in from various districts across the northwest showed that more than 800 people had died due to the flooding. Many people remain missing.

Floodwaters were believed to be receding in some sections, but it was difficult to get a complete picture.

In the Nowshehra area, scores of men, women and children sat on roofs in hopes of air or boat rescues.

"There are very bad conditions," said Amjad Ali, a rescue worker in the area. "They have no water, no food."

A doctor treating evacuees at a small relief camp in Nowshehra said some had diarrhea and others had marks appearing on their skin, causing itching.

Children and the elderly seemed to have the most problems, Mehmood Jaa said.

"Due to the floodwater, they now have pain in their bodies and they are suffering from fever and cough," Jaa told the news agency.

Rescuers were using army helicopters, heavy trucks and boats to try reaching flood-hit areas, the U.N. said. It reported that thousands of homes and roads were destroyed, and at least 45 bridges across the northwest were damaged.

The destruction is slowing the rescue effort, said Luther Rehman, a government official in Khyber-Pakhtunkhwa, the northwest province.

"Our priority is to transport flood-affected people to safer places. We are carrying out this rescue operation despite limited resources," he said, adding they needed more helicopters and boats.