"This is quite a big accident. Rescue teams have reached on site and at least 15 passengers were killed and 45 injured," Khawaja Saad Rafique told reporters.
"More rescue teams have been dispatched to the site."
The derailment happened near Sahara railway station in the city of Nawabshah in the southern Sindh province, local media reported.
"The Hazara Express was travelling from Karachi to Abbottabad, eight coaches have derailed," Mohsin Syal, a railway official, told HUM News.
Ijaz Shah, a provincial railway official, told AFP that several passengers were killed and that a relief train has been dispatched to the site.
Images posted to local media show dozens of people at the site, with some smashing windows to help passengers clamber out of the twisted carriages and at least one coach overturned.
Accidents and derailments occur frequently on Pakistan's antiquated railway system.
In June 2021 two trains collided near Daharki in Sindh killing at least 65 people and injuring about 150 others.
In that accident, an express derailed onto the opposite track, and a second passenger train crashed into the wreckage roughly a minute later.
At least 75 passengers burnt to death in a fire aboard the Tezgam express train in October 2019, while a two-train collision at Ghotki killed more than 100 people in 2005.
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