A gunman has killed two people at a Wisconsin casino and seriously wounded a third before he was killed by police, in what authorities said appeared to be a targeted attack.

Brown County Sheriff’s Lt Kevin Pawlak said investigators believe the gunman was seeking a specific person.

“He was targeting a specific victim who was not there, but he decided to still shoot some of the victim’s friends or co-workers, it appears,” Lt Pawlak said.

Neither the gunman nor the shooting victims were immediately identified.

Lt Pawlak was not sure if the gunman was a former employee of the restaurant, but said “it appears there’s some relationship that had to do with employment”.

“Whether or not they all worked there, we’re still working on,” he said.

The wounded person was being treated at a Milwaukee hospital, Lt Pawlak said.

The attack happened at around 7.30pm on Saturday at the Oneida Casino operated by the Oneida Nation on the western side of Green Bay, with the casino tweeting that an active gunman was on the scene.

Jawad Yatim, a witness, said he saw at least two people shot.

“I know for sure two, because it happened right next to us, literally right next to us,” Mr Yatim said. “But he was shooting pretty aggressively in the building, so I wouldn’t doubt him hitting other people.”

Attorney General Josh Kaul tweeted shortly before 10pm that the scene was “contained. There is no longer a threat to the community”.