A police spokesman said part of State Highway 25 at Kopu, just outside of Thames, had been cordoned off while armed police searched a local address.
"We're looking for a particular person," he said.
"The AOS was dispatched due to the nature of the information we had on the earlier incident."
A fire service spokesman said there had been reports of smoke coming from the vicinity of the police cordon but crews on the ground could not see any.
Kopu Station Hotel duty manager Harley Ferguson said there had been a great deal of commotion around the area.
"There's just cops walking around in the middle of the roads with guns," he said.
One customer, who did not wish to be identified, said at 4.55pm that he "heard a couple of gunshots a couple of hours ago".