The police chief of Bahawalpur, Suhail Tajik, says Tuesday's accident took place on a section of the highway outside the city.
He says the passenger van was overtaking another vehicle when it slammed into an oncoming truck. The van was completely destroyed.
Rescuers moved 10 injured passengers to the city hospital. All were in serious condition.
Pakistan has a well-developed highway system but drivers often ignore basic safety rules.