A school picnic at a dam has ended in tragedy during a horror day in which 51 people were killed in two separate accidents in Pakistan.

At least 10 young pupils died in a mass drowning when their boat capsized, while eight are still missing. They were aged between seven and 12 years old.

The victims were part of a group of about 25 from a religious school who ventured onto the water during an outing at Tanda Dam in Khyber Pakhtunkhwa in the north.

Separately, at least 41 people were killed when their bus plunged off a bridge and crashed into a ravine, bursting into flames.

The victims were incinerated “beyond recognition” in the fiery accident which had few survivors, said district police officer Israr Umrani.

All that was left of the bus was a shell of mangled metal. DNA would be needed to identify the victims, said an official.

The burnt passenger bus after plunging off a bridge. Photo: Getty

The bus carrying 48 passengers was on its way to the southern city of Karachi from Balochistan’s capital of Quetta.

Footage shows dozens of people combing through the wreckage and ambulance workers carrying a dead body out of the debris.

Assistant Commissioner Hamza Anjum for Lasbela told Dawn newspaper the vehicle had crashed into a bridge, causing it to fall into a ravine and catch fire.

There were reports the vehicle had hit a pillar before plunging off the road.

Fatal road accidents are common in Pakistan, where traffic rules are rarely followed and roads in many rural areas are in poor condition.

At least 22 people were killed in June, including nine members of one family, when a passenger van fell into deep ravine in Balochistan.

At the lakeside boating accident, officials said eight students were still missing while seven of the injured had been taken to hospital.

Twenty-five children had ventured out on the dam which was closed by authorities for recreational trips.

Pakistani military divers were helping with the rescue and recovery efforts.

Video footage by local broadcasters and on social media showed rescuers in the water.

Mass drownings occur frequently in Pakistan due to over-crowded and aged vessels, and the fact many people cannot swim.

A crowd gathers beside Tanda Dam after the boating accident. Photo: Getty