Levesque says a rear-end collision between two vehicles pushed one car into oncoming traffic and it collided head-on with the bus carrying passengers to a casino.
The total number of injured was initially thought to be 22, but has been reduced.
Two of the critically injured are the bus driver and the person in the car that struck it.
One other person with critical injuries and seven with minor injuries have been taken to hospitals.
The Associated Press contributed to this story.