The deceased have been identified as Md. Babu, 40, a CNG driver from Harigacha village in Natore Sadar upazila and CNG passenger Md Sagar, 25, a student of the Department of Environmental Science at Jahangirnagar University. The identities of the other duo could not be confirmed immediately.
The accident occurred around 5:15pm in the Banbelgharia bypass area of Natore city, said Sub Inspector Md Abul Kalam of the Highway Police's Jhalmalia outpost.
He said the three-wheeler was going to Natore from Rajshahi when it collided head-on with a Rabbi Paribahan passenger bus coming from opposite direction from Sirajganj to Rajshahi, leaving Sagar dead on the spot and three others critically injured.
Fire fighters rushed to the scene, rescued the injured and sent them to Natore Sadar Hospital, where driver Md. Babu later succumbed to his injuries, added Abul Kalam.
The other two critically injured were transferred to Rajshahi Medical College Hospital where they breathed their last at night.
The bus driver and his assistant fled the scene immediately after the accident. However, police have seized the bus and are preparing to file a case in connection with the incident, reports BSS.