Local residents heard gunshots and screams from a garden where the cockfight took place, according to Cong An Nhan dan website, the Ministry of Public Security’s official mouthpiece.
“There was a quarrel over cockfight betting which led to the shooting,” the website reported.
State-run VNExpress news site said the suspected shooter fled the scene on a motorbike and was arrested later Wednesday.
Police refused to comment when contacted by AFP.
Gun violence is extremely uncommon in Vietnam, where it is illegal for citizens to own firearms and the black market for weapons is limited.
Betting on cockfights is also illegal, although the pastime is ubiquitous underground in the gambling-mad country.
In a rare shooting in 2016, two senior officials in northern Yen Bai province were killed by a colleague at their office, before the gunmen shot himself.
AFP