The mishap occurred in the Manopad police station limits around 2 AM.
The lorry, while trying to overtake the tractor, hit it from the rear side, resulting in a boiler on the tractor falling on the victims, they said.
In the accident, four agricultural labourers from Kurnool district-- P Venkataramlu (53), B Mallanna (35), Sambasivadu (53) and Ashok (23), died on the spot while another person was injured, police said.