The victims were returning to their village after a holy dip in Narmada river at Dharaji in Dewas district, police said.
The mishap occurred when the speeding bus was trying to overtake the tractor-trolley and in the process hit it from behind.
Four of the seriously injured persons were shifted to Indore's government MY hospital for treatment, they said.
The bus driver fled from the spot after the mishap, police said, adding that a case has been registered in this regard.