The incident occurred this afternoon along the East-West highway in Nawalparasi district when the bus en route to Kathmandu from Sunauli on the Nepal-India border collided with the ambulance and the bike coming from the opposite direction, police said.
Seven people were killed and twenty one passengers were injured in the road mishap, with six people in critical condition, authorities said.
Among those killed six were women, the police said.
The injured are receiving treatment at Devdaha Medical College and Lumbini Medical College.