On Monday evening Duong Van Han appeared on a street in Chau Doc Town with a homemade machete, waved it around and threatened to attack people with it.
A team of police officers arrived on the scene soon to stop Han.
They tried vainly to convince him to drop the weapon.
Major Thai Van Tam, one of the officers, then approached Han with a long iron rod.
Han fiercely attacked Tam and wounded him in his right arm. Several people filmed the act.
After a while the officers managed to overpower Han and seize the weapon.
The police said he was in a state of panic when arrested. It is not clear if he was high on drugs.
Tam lost a lot of blood but is now in stable condition at a local hospital.