The accident occurred on a busy highway in Bahawalpur.
The van, which was going to Ahmedpur Sharqia from Bahawalpur, collided head-on with the truck.
Twelve people were killed instantly and 12 others died in hospital, the officials said.
Seven women and three children were among the dead.
Several people were injured and some of them were in a critical condition, the officials said.
Rescue teams had to cut through the mangled metal of the van to remove bodies and the injured.
Lahore: At least 24 people, including women and children, were killed and several others injured when a van collided with a speeding truck in Pakistan's Punjab province Tuesday, officials said.
First Published: Tuesday, October 30, 2012, 14:16