Pakistani disaster relief officials issued fresh flood warnings Sunday after the death toll from heavy monsoon rains rose to 45 and waters paralysed parts of the largest city Karachi.

Flash floods caused by monsoon downpours have inundated some main roads in the sprawling port city and swept away homes in the northwestern province of Khyber Pakhtunkhwa.

In neighbouring Afghanistan, flash floods caused by days of torrential rain have killed more than 40 people, mostly in Surobi district east of Kabul.

Pakistan's National Disaster Management Authority warned that more thunderstorms and heavy rains were expected on Monday and some rivers may flood.

At least 45 people have been killed in the floods over the weekend. Officials in Karachi said at least 19 had died in the city to add to 20 dead in the northwest and six in the southwestern province of Baluchistan.

Doctor Semi Jamali at the Jinnah Hospital in Karachi told AFP that most of the deaths occurred due to electrocution or collapsing roofs and walls.

Army engineers helped relief efforts in Karachi on Sunday where roads and streets were flooded and the city was practically paralysed, an AFP reporter said.

Authorities in the city of 18 million people, which contributes 42 percent of Pakistan's GDP, said it would take more than two days to clear up after the water flooded markets, buildings and houses and blocked roads.

Hundreds of cars were seen half-submerged after poor sewerage and drainage systems choked due to garbage.

Prime Minister Nawaz Sharif sent three of his cabinet ministers to inspect damage in flood-hit areas.

Pakistan has suffered devastating monsoon floods for the last three years, including the worst in its history in 2010 when catastrophic inundations killed almost 1,800 people and affected 21 million.

Flash floods in Afghanistan kill more than 40
Kabul, Kaboul (AFP) Aug 04, 2013 - Flash floods triggered by days of torrential rain have killed more than 40 people in Afghanistan, destroying dozens of houses, a senior disaster official said Sunday.

Heavy flooding that began three days ago hit nine eastern and southeastern provinces and some districts of the capital Kabul.

Surobi district of Kabul was the hardest hit, Ghulam Farooq, the head of emergency operations for Afghanistan's National Disaster Management Authority, told AFP.

"The primary report indicates that 35 people have died in Surobi district, eight in Khost and one in Kapisa," he said.

Four people were missing in eastern Nangarhar province, he added.

The floodwaters also destroyed hundreds of hectares of farmland and displaced hundreds of people in those provinces, he said.

"At least 237 houses have been destroyed in Surobi alone," he said.

He said emergency teams had been sent to the areas to assess the situation.

Harsh winters in Afghanistan and heavy snowfalls often cause swollen rivers that trigger flooding in the mountainous country in spring and summer.

But this year, Afghanistan witnessed one of the hottest summers in decades with temperatures reaching up to 50 degrees Celsius in some parts.

Across the border in Pakistan floods have also killed 45 people with disaster relief officials warning more rain was on its way.

Flash floods caused by monsoon downpours have inundated some main roads in the sprawling port city of Karachi and swept away homes in the northwestern province of Khyber Pakhtunkhwa.