The attack on Wednesday saw the group of men, armed with high-caliber weapons, storm a Banco do Brasil bank, the Para state security ministry said.
Images on social media showed a firefight in the streets of the town. The robbers killed one hostage during the heist, the ministry added, while another local resident was shot in the leg and is in a stable condition in hospital.
"We pray to God to comfort the family of the young man who lost his life," Cametá Mayor Waldoli Valente wrote on Facebook.
The security ministry said it had found one abandoned getaway vehicle outside the town with explosives inside. The town was now calm, it added, with police reinforcements arriving by plane and boat.
It was not immediately clear how many hostages had been taken or if they were all freed. Authorities also did not say how much money was stolen from the bank.