Sub-Divisional Police Officer Mahendra Basantri said the mishap took place as the speeding truck hit the auto rickshaw on the rear.
The auto rickshaw was carrying nine passengers from Madanpur to Taradih and three of them died on the spot, he said adding one escaped unhurt.
Four injured persons were admitted to the Anugrah Narayan Medical College and Hospital, while another was discharged after first-aid at the nearby primary health centre.
The truck driver escaped with the vehicle after the incident, he added.
