At least 10 cars of a passenger train derailed in Pakistan's southern Sindh province on Sunday, killing at least 30 passengers while injuring over 100 others, government and police officials said.

While confirming the casualties, Sindh's Chief Minister Syed Murad Ali Shah said that nine cars have been cleared, adding that a rescue operation is underway in the remaining car to recover passengers.

He said that critically injured people will be transported to the southern port city of Karachi for better treatment.

The Hazara Express train, comprising around 16 to 17 cars with over 1,000 passengers, veered off the track while crossing a canal bridge on its way to the country's northwest Khyber Pakhtunkhwa province from Karachi.

Minister for Railway Khawaja Saad Rafique told the media that authorities are investigating the incident and the possibility of "sabotage" can be ruled out.

Rescue teams, the Pakistan Army and Pakistan Railways personnel rushed to the site and initiated relief activities. Local volunteers also helped rescue the stranded passengers.

Affaq Rao, an eyewitness, told Xinhua he was working in the fields when he heard a strange loud bang.

"It was the noise of the train derailing. Initially, I could not figure out what to do, but then along with other locals, I ran towards the coaches and tried helping people get out of the train," he said.

"These were the most horrific and heart-wrenching scenes of my life," Rao said.

Rehman Malik was traveling to the eastern city of Rawalpindi for his business venture when the unfortunate incident happened. "Fortunately, I remained unhurt," he said.

Malik, who received minor injuries in the accident, said that the incident was his worst nightmare.

After the train derailment, train operations were suspended, affecting the routine of many trains, with railway authorities saying that it may take up to 18 hours to restore operations.

Pakistani Prime Minister Shahbaz Sharif expressed deep grief and sorrow over the incident, and directed the authorities to provide the best medical treatment to the injured people.