Footage on Pakistani TV showed two elderly men in the Peshawar area, clinging to a fence post as a raging torrent swept over their heads.
Our correspondent also reported that many people were trapped in the gushing rivers.
At least 10 people died near Peshawar when their homes collapsed, Adnan Khan, spokesman for the northwest province's Disaster Management Authority, said.
Dozens of people were still believed missing, so the overall death toll was expected to rise.
Monsoon season often leads to widespread flooding in Pakistan, which has many low-lying villages.
The ongoing rain and bad weather are also suspected factors in Wednesday's plane crashnear Islamabad that killed all 152 passengers on board.