Al Jazeera's Sohail Rahman, reporting from Pakistan's capital Islamabad, said the city experienced "a deluge of water" that came in from Khyber Pakhtoonkhwa [the new name for North West Frontier Province].
"The floods have really affected the infrastructure in and around the province," our correspondent said.
"The people in the affected areas were quite critical in the first 24 hours, saying that the authorities were not doing enough.
"The problem has been getting the help to them," he said.
Northwest hit hardest
The northwest appeared to be the hardest hit, Mian Iftikhar Hussain, the information minister for the province, said.
At least 291 people died in various parts of that province over the last three days, Mujahid Khan of the Edhi Foundation, a privately run rescue service that operates morgues and ambulances across the South Asian country, said.
In Pakistani-administered Kashmir, at least 22 people had been confirmed dead as of Thursday evening, Sardar Attique Khan, the area's prime minister, told reporters.
The tolls from the deluge were expected to rise because many people were still missing.
Poor weather this week also may have been a factor in Wednesday's Airblue plane crash that killed 152 people near the Pakistani capital, Islamabad.
In the Swat Valley, residents were forced to trudge through knee-deep water in some streets.
A newly constructed part of a dam in the Charsadda district collapsed, while the UN said it had reports that 5,000 homes were underwater in that area.
Hussain estimated 400,000 people were stranded in various northwest villages.
Lack of boats
"A rescue operation using helicopters cannot be conducted due to the bad weather, while there are only 48 rescue boats available for rescue," he said.
Pakistan's poorest residents are often the ones living in flood-prone areas because they can't afford safer land.
Southwest Baluchistan province has also been hit hard by the recent rains.
Last week, flash floods in that region killed at least 41 people and swept away thousands of homes.
The UN in a statement on Thursday said 150,000 people were affected there.