Flash flooding caused by torrential monsoon rains has killed at least 28 in Pakistan and affected hundreds of thousands of people, according to aid agencies, with further downpours expected in the coming days.

In Chitral in the northwest, roads, bridges and crops were badly damaged, with more than a quarter of a million affected, the EU's humanitarian office said.

Pakistan's poorest province, Baluchistan in the southwest, was also badly hit.

"Some villages have been cut off from the rest of the district," said Shah Fahad Ali Khan, 27, a university lecturer living in Zargrandeh, a village in Chitral.

People in flood-prone areas have been shifted to safer ground, he said on Friday in an online message.

Heavy rains are expected over the weekend, which may cause more flash flooding and could trigger landslides in Khyber Pakhtunkhwa province, which includes Chitral, Pakistan's meteorological department said earlier this week.

The heavy rains started falling on July 15, and continued over the next week throughout the country, causing some urban flooding in Lahore, Islamabad and Rawalpindi, the Pakistani Red Crescent said in a statement.

Deadly flooding is common in Pakistan's monsoon season, which runs from June to September. Last September dozens of people in Punjab and Kashmir were killed when flash floods caused their homes to collapse.

In 2010, the worst floods in memory affected killed more than 2,000 people in Pakistan, with damage to infrastructure running into billions of dollars, and huge swathes of crops destroyed as a fifth of the country was inundated.

Prime Minister Nawaz Sharif has announced a $5 million aid package for Chitral, and visited flood relief camps in Punjab province on Friday, local media reported. - Reuters