Residents and rescue workers gather near the site after a passenger train collided with a cargo train in Sadiqabad. Reuters
Ahmed said some of the injured passengers were listed in critical condition.
Prime Minister Imran Khan quickly ordered authorities to provide best possible medical care to the victims. In a statement, he said he was saddened by the news.
Khan ordered Railways Minister Sheikh Rashid Ahmad to "take emergency steps to counter decades of neglect of railway infrastructure" and ensure safety standards.
Authorities said Pakistan's army was also taking part in the rescue efforts.
"Have asked Railways Minister to take emergency steps to counter decades of neglect of railway infrastructure and ensure safety standards.
Train accidents are common in Pakistan mainly because of poor railway infrastructure and negligence of railway authorities.
Prime Minister Imran Khan issued a statement of condolence in which he blamed the infrastructure of Pakistan's colonial-era railway network which has fallen into disrepair due to chronic under-investment and poor maintenance.
"Have asked Railways Minister to take emergency steps to counter decades of neglect of railway infrastructure and ensure safety standards," Khan tweeted.
Last month, six people were killed when a freight train collided with a passenger train in Hyderabad 165 km (100 miles) from Karachi.
The cause of Thursday's crash is under investigation but Railways Minister Sheikh Rasheed Ahmed said human error was believed to be responsible.
"I have ordered an inquiry. Investigation will complete in two-three days," he told Geo Television.
The minister also announced compensation for the dead and injured.
The Akbar Express, heading to the western city of Quetta from Lahore, crashed into the freight train in the Sadiqabad area of Punjab province's southern Rahim Yar Khan district, destroying five carriages and trapping passengers.
The death toll from a train collision in central Pakistan rose to 23 on Friday after several people succumbed to their injuries overnight, officials said. The incident took place on Thursday
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The official confirmed there were 16 Pakistan army personnel on the bus and said most passengers were from Skardu or other parts of Gilgit-Baltistan.