Youngsters wade through a flooded street caused by heavy rain in Peshawar, Khyber Pakhtunkhwa province, on Monday. AP

At least 41 people have died in storm-related incidents across Pakistan since Friday, including 28 killed by lightning, officials said on Monday, as authorities in the country's southwest declared a state of emergency.

Most of the deaths occurred when lightning struck farmers harvesting wheat and rains caused houses to collapse in eastern Punjab province, said Arfan Kathia, a spokesman for the provincial disaster management authority. He said more rains were expected this week.

Pakistan's National Disaster Management Authority (NDMA) has warned of landslides and flash floods because more rain is expected in coming days. Punjab, Pakistan's largest and most populous province, witnessed the highest death toll, with 21 people killed by lightning between Friday and Sunday.

"I have asked the NDMA to coordinate with the provinces... and for the NDMA to provide relief goods to areas where damages occurred," Prime Minister Shahbaz Sharif said on Monday. People living in open, rural areas are more at risk of being struck by lightning during thunderstorms.

 Rescue workers and locals gather to clear the rubble of a house partially damaged by landslide due to heavy rainfall in Matta, a town in Swat Valley, Pakistan. AP

Rain also lashed the capital, Islamabad, and killed eight people in southwestern Balochistan province over the weekend, and eight others died in northwestern Khyber Pakhtunkhwa province bordering Afghanistan.

Rainwaters flooded streets in the northwestern city of Peshawar and in Quetta, the capital of Baluchistan, where authorities declared a state of emergency.

Schools in the province were ordered shut on Monday and Tuesday, delaying the return of students after Eid Al Fitr holidays at the end of the holy fasting month of Ramadan. Four people were killed in road accidents linked to flooded roads in southern Sindh province.

Another eight people were killed in the northwestern province of Khyber Pakhtunkhwa, including four children, when houses collapsed in the heavy downpours.

Due to inclement weather in Karachi, several flights have been cancelled and some have faced delays. A rain emergency has been declared in operational sections, including the Airside Section, by the Civil Aviation Authority (CAA).

According to airport sources, multiple flights were cancelled and experienced delays due to the adverse weather conditions in Karachi on Sunday.

Reportedly, PIA flight 503 from Karachi to Gwadar and the PIA's flight PK 768 from Karachi to Islamabad were cancelled. Private airline flights from Karachi to Lahore and Karachi to Islamabad were also cancelled, as per airport sources.

PK-308 from Karachi to Islamabad also experienced delays, while a flight from Iraq to Karachi could not operate due to tensions between Iran and Israel.

Pakistan Peoples Party chairman Bilawal Bhutto Zardari, speaking to local media, blamed climate change for the surge in lightning incidents.

Pakistan is increasingly vulnerable to unpredictable weather patterns, as well as often destructive monsoon rains that usually arrive in July.

Agencies