Heavy rain that started on Friday has spread destruction in several northern districts, with most people killed in flash floods, according to the National Disaster Management Authority.
In hilly areas, the rain caused flash floods as well as mud and rock slides that washed away houses, buildings, vehicles and belongings.
Buner district was the worst hit, with more than 200 deaths.
Heavy rain in the flood-hit areas, including Buner, forced rescue teams to halt relief efforts for several hours on Monday, a regional government officer, Abid Wazir, told Reuters.
"Our priority is now to clear the roads, set up bridges and bring relief to the affected people," he said.
Relief goods have been sent to the affected areas, Information Minister Attaullah Tarar told local Geo News television.
Food, medicine, blankets, camps, an electric generator and de-watering pumps are included in the relief goods, the disaster management authority said in a statement.
Buner, a three-and-a-half-hour drive from the capital Islamabad, was hit by a cloudburst, a rare phenomenon in which more than 100 millimetres of rain falls within an hour in a small area, officials said.
In Buner, there was more than 150mm of rain within an hour on Friday morning, they said.
More heavy rain is expected across Pakistan until early September.
"The current weather system is active over the Pakistan region and may cause heavy to very heavy rainfall during the next 24 hours," the disaster management authority said on Sunday.
Torrential rain and flooding this monsoon season have killed 657 people across Pakistan since late June, the authority said.
