Several media outlets reported officials confirmed at least 55 people died but the BBC said one person counted at least 100 bodies.
Kogi state police said the truck barreled down a hill at high speed, crashing into several vehicles before smashing into the crowded market in the village of Allo, killing dozens and injuring about 40 people.
Media outlets said it wasn't clear whether the accident occurred Friday or Saturday. CNN reported it occurred late Friday.
Austin Aipoh, the government's road safety commander in Kogi state, said the cause of the crash was being investigated but a preliminary exam indicated faulty brakes may have led to the crash.
Ibrahim Idris, the governor of Kogi, declared three days of mourning.