At least 30 people have been killed and 100 injured when a train derailed in southern Pakistan, a police spokesman has confirmed.

Several carriages of the Hazara Express overturned near Sahara railway station in Nawabshah, about 275km (171 miles) from the largest city Karachi.

Wounded passengers were moved to nearby hospitals. Rescue teams are trying to free people from the twisted wreckage.

Accidents on Pakistan's antiquated railway system are not uncommon.

Videos posted on social media showed dozens of people at the site of the accident, with some passengers climbing out of the overturned carriages.

One passenger who survived told BBC Urdu he had seen many women and children lying on the ground.

"They were shouting and screaming. I didn't know what to do. I filled my hands with water from this canal nearby and poured it on the faces of those who were unconscious, hoping they would regain consciousness," Naseer Ahmed said.

Nasser said he survived the accident because he "fell out of the window when the train derailed".

Aslam, who was on the train with his son, said: "We were sleeping when suddenly the carriage came down and [it felt like] an apocalypse."

Railway Minister Saad Rafiq said initial investigations showed the train was travelling at normal speed and they were trying to establish what led to the derailment. It could be the result of a mechanical fault or sabotage, he added.

Authorities have dismissed reports the track was flooded.

A railways spokesperson in Karachi said at least eight carriages went off the track.

He said military and paramilitary troops along with rescue workers were on the scene and helped to rescue passengers trapped inside the train carriages.

The most seriously injured passengers were transported to distant, better-equipped hospitals in military helicopters.

Officials said rescue operations were completed in the early evening on Sunday.

An emergency has been declared in the main hospitals in Nawabshah and neighbouring districts of Sindh.

Train services to the interior districts of Sindh have been suspended.

Sindh Information Minister Sharjeel Memon told BBC News that the government's top priority was "the rescue work, which we are totally focused on".

In 2021, two trains travelling in Sindh province collided, killing at least 40 people and injuring dozens.

Between 2013 and 2019, 150 people died in such incidents, according to local media reports.