A family wades through a flooded street caused by heavy monsoon rains in Karachi on Sunday. AP

Nearly two-dozen people have been killed in the Pakistani city of Karachi after heavy monsoon rains inundated most parts of the metropolis, officials and rescuers said on Sunday.

Most deaths were caused by electrocution and falling roofs in the city of 20 million people, German news agency DPA quoted local official Ali Sajjad as saying.

A woman works in her kitchen in her flooded house after heavy monsoon rains in Karachi on Sunday. AFP

At least 23 deaths have been reported since the rain started on Saturday night and continued until Sunday afternoon, said Anwar Kazmi from the private Edhi rescue agency.

The death toll was expected to rise as roads and streets were still flooded in some parts of the city, making it impossible for rescuers to reach the victims, Kazmi added.

The military was assisting the civil administration in pumping the water out of the inundated streets, an army spokesperson said.

The metrological department's Sardar Sarfraz predicted more spells of rain, but said they would not be intense.

An overloaded bus drives through a flooded road caused by heavy monsoon rains in Karachi on Sunday. AP

The heavy rains are expected to hit the central province of Punjab on Monday when the Muslim majority country is scheduled to celebrate the religious festival of Eid Al Adha.

A similar deluge might hit different cities in Punjab, the National Disaster Management Authority, NDMA, warned on Sunday.

Hundreds of people are killed across South Asia by flash floods and the inundation of cities during the monsoon, a rainy season in July and August.

The phenomenon of global warming has intensified these threats, the DPA report quoted environmentalist Qamar Zaman Chaudhry as saying.

WAM