At least 40 people have been killed as a result of heavy monsoon rains in Pakistan, officials have said, as country's meteorological office warned of more rain and thunderstorms in the coming 72 hours.

Most of the deaths came in roof collapses in Punjab, Pakistan's most populous province, with 14 people killed in the provincial capital Lahore.

"At least 28 people have been killed in different incidents of roof collapses in Punjab province during the last 24 hours," Jam Sajjad, a spokesman for rescue services told AFP news agency.

He said the dead included women and children, and 28 people had been injured.

Rizwan Naseer, the director general of rescue services in Punjab confirmed the toll and said the injured were being moved to hospitals.

"We have been removing the debris to search for survivors and the injured," Naseer said, adding that the toll was likely to rise as more information came in from around the province.

In Pakistan-administered Kashmir, 10 people were killed and four others injured, disaster management agency chairman Akram Sohail told AFP.

He said there had been some flash flooding in the Himalayan territory and warned that the rivers Jhelum and Neelum were close to overflowing in some places.

Flood waters also swept an overcrowded bus carrying a wedding party into a gorge with all but six of the 50 on board feared dead in India-administered Kashmir, officials said.

Rescue teams have been deployed to the flooded gorge south of Kashmir's main city of Srinagar but they have so far been unable to reach the bus, police said.

The government has been criticised for not doing more to mitigate against the dangers posed by seasonal rains washing away homes and farmland.

Pakistan has suffered deadly monsoon floods for at least the last four years. Last year, 178 people were killed and around 1.5 million affected byflooding around the country.

The floods of 2010 were the worst in Pakistan's history, with 1,800 people killed and 21 million affected in what became a major humanitarian crisis.