The Lahore-bound bus collided with a speeding truck at Jehanian, located 330 km from the capital of Punjab province, an official of the Highway Police Patrol said.
Four of the fishermen sustained minor injuries and police took them to a nearby hospital where they were provided first aid, he said.
The fishermen had boarded the bus in Karachi on Sunday after being freed from a jail in the southern port city.
They were to be handed over to Indian authorities at the Wagah land border crossing on Monday. Following the accident, their repatriation was put off till Tuesday, officials said.
Leading rights activist Ansar Burney, whose trust provided the bus that was transporting the fishermen, said arrangements were made to send them to Lahore in another vehicle.