Pakistani officials said the death toll was likely to increase as rescue crews were still trying to access several mangled coaches.
The accident in the Ghotki district of the southern Sindh province took place when eight compartments of the northbound Millat Express train derailed and were hit by another train, the Sir Syed Express, near Dharki.
About 25 people were believed to be trapped, according to local media outlets.
“Shocked by the horrific train accident at Ghotki early this morning leaving 30 passengers dead. Have asked Railway Minister to reach site & ensure medical assistance to injured & support for families of the dead. Ordering comprehensive investigation into railway safety faultlines,” tweeted Prime Minister Imran Khan.