Some of the victims were struck by lightening while the others were swept away by the rushing waters after heavy rains accompanied by thunder storms lashed Dir district, 300 kilometers (188 miles) north of Peshawar, district chief Sahibzada Tariqullah said.
A provincial government statement later said 20 people were also injured while six were missing.
The worst hit areas were Warri, Barkand and Gandi Gari villages in Nihag Darra town where flooding washed away several mud buildings leaving hundreds of people homeless.
Officials said they were facing delays in starting rescue work because of the difficult terrain.
Pakistan's southern and southwestern regions were hit hard by monsoon rains last month which killed at least 167 people and made more than one million homeless.