The accident occurred in Rahim Yar Khan district, 400 km from Lahore, the capital of Punjab.
Local residents said the bus carrying 45 passengers was going to Karachi when it hit a fence.
Rescue teams reached the spot and took the injured to a nearby hospital, where doctors confirmed they had received 20 bodies.
The death toll might rise as 10 injured were in a critical condition, officials said.
Lahore: At least 20 people, including women and children, were killed and several others injured when a bus met with an accident in Pakistan's Punjab province on Friday, police said.
First Published: Saturday, May 26, 2012, 00:32