The drivers of both the vehicles were killed, they said.
The state transport bus belonging to Ferozepur depot started its journey from Ferozepur City at 7.20 am towards Sri Ganganagar in Rajasthan with 22 passengers on board.
As soon as the bus reached near village Kari Kalan, it collided with the truck that was coming from the Fazilka side, police said.
Eyewitnesses told the police that the driver of the bus wanted to overtake a vehicle, but due to poor visibility owing to dense fog, he could not see the truck that was coming from the opposite direction.
More From This Section
Earlier, police quoting initial reports had said that at least six persons had died in the accident.
Punjab Chief Minister Amarinder Singh announced Rs 1 lakh ex-gratia for each for the kin of those killed in the accident.
He directed the district authorities to provide free medical treatment to the injured, an official spokesperson said in Chandigarh.
The chief minister directed the district civil and police administration to extend all possible help to the family members of the deceased, the spokesperson said.