QUETTA, PAKISTAN -- A passenger bus crashed into a pillar and fell off a bridge, catching fire and killing 40 people in southern Pakistan on Sunday, a government official said.

The bus was carrying 44 passengers from Quetta in Balochistan province to Karachi in neighboring Sindh province. The accident was near the town of Bela, in Lasbela district.

Hamza Anjum Nadeem, assistant commissioner in Bela, said the bodies of 40 people, including women and children, were recovered. Four injured passengers were rescued.

"The accident happened due to over-speeding and the bus crashed into the pillar of a bridge. It caught fire soon after falling (off the bridge)," he said.

Images from the crash site showed what was left of the charred bus lying near the bridge. The recovered remains of some of the dead are lined up in rows nearby.

Nadeem said the bodies were charred beyond recognition and are being transported to Karachi for DNA sampling. After identification, the bodies will be handed over to the victims' relatives.

Firefighters and workers from the Lasbela Welfare Trust and the Edhi Welfare Foundation carried out the rescue operation.

The chief minister of Balochistan, Mir Abdul Qudoos Bizenjo, expressed his sorrow for the loss of life and ordered authorities to provide the best medical facilities to the injured.

Traffic accidents in Pakistan generally happen due to violation of traffic rules, resulting in the deaths of thousands every year.

In a separate incident, in Pakistan's northwest, at least 10 students who were on a picnic drowned after their boat capsized in a lake on Sunday, police said.

The children, from a religious school in Khyber Pakhtunkhwa province, were visiting a lake at Tanda Dam.

Local police official Qismat Khan said 25 students were on the boat. Six were rescued, and three of them are in critical condition. The dead pupils were aged between 11 to 13. Nine children remained missing.

Khan said an earlier group of 16 students was able to cross the lake. But the same boat capsized while taking 25 on the next trip. "As per initial reports, overloading resulted in the overturning of the boat," he said.

Abdul Rauf Qaiserani, the district police officer, reached the scene to oversee the rescue work.

Life-saving divers were called in from the provincial capital Peshawar due to an immediate lack of them locally. People from the area joined authorities in recovering bodies from the water.

Pakistan has witnessed similar incidents in the past as tourist attractions do not adhere to safety measures, including the use of life vests.