ISLAMABAD — Two express trains collided in southern Pakistan early Monday, killing at least 30 passengers, authorities said, as rescuers and villagers worked to pull injured people and more bodies from the wreckage.

Several people have been injured after the Sir Syed Express train collided with the Millat Express train in Sindh province between railway stations, according to railway officials.

At least 30 people are dead and officials are working to rescue at least 17 people who remain trapped, Edhi Rescue Services said. So far, 23 people have been rescued, the rescue service added.

Between 15 to 20 passengers are still trapped in the wreckage of the Millat Express train and authorities were trying to arrange heavy machinery to rescue those people who are crying for help, said Umar Tufail, a police chief in Ghotki district in Sindh province, where the collision occurred before dawn.

The Millat Express derailed and the Sir Syed Express train hit it soon afterward, said Usman Abdullah, a deputy commissioner in Ghotki. It wasn’t immediately clear what caused the derailment and the subsequent collision.

“Right now the challenge for us is to quickly rescue those passengers who are still trapped in the wreckage," he said.

Abdullah said so far 30 people had died. According to railway officials, about 1,100 passengers were on board the two trains, and arrangements were being made to help the surviving passengers.

Pakistani Prime Minister Imran Khan tweeted condolences for the victims of Monday's train crash and said that he was ordering a comprehensive investigation into railway safety.

"Shocked by the horrific train accident at Ghotki early this morning leaving 30 passengers dead," Khan tweeted, adding that he had asked the Railway Minister to ensure the injured received medical attention and the families of the dead received support.

According to local media, some of the passengers were traveling by the Millat Express train to attend a wedding party but it was unclear whether they were among the dead or injured.

TV footage showed ambulances transporting injured passengers to hospitals. According to Pakistani TV stations, heavy machinery had not reached the scene about four hours after the crash.

Officials at Pakistan railways said they had ordered an investigation and rescue work was still in progress. Some of the injured passengers were listed in critical condition at a hospital.

Authorities said troops had also arrived at the scene of the accident to participate in the rescue work.

Malik Aslam, a local villager, told Pakistan's Geo News TV that about 100 people were injured and he counted at least 30 bodies of passengers during the rescue and recovery work.

Train accidents are common in Pakistan, where successive governments have paid little attention to improving the poorly maintained signal system and aging tracks.

In 1990, a packed passenger plowed into a standing freight train in southern Pakistan, killing 210 people in the worst rail disaster in Pakistan’s history. — Agencies