According to police officials, the driver of the passenger bus apparently lost control and crashed into the van coming from the opposite direction.
"The accident took place near the Lucky Shah Saddar area near Sehwan town," an official said.
Thousands of devotees visit Sehwan every year to pay homage at the shrine of Sufi saint Lal Shahbaz Qalander on the outskirts of the town.
However, the nature of the accident and exact number of passengers in both vehicles is yet to be confirmed.
Rescue officials said around 20 injured were shifted to a nearby hospital.