The Armed Offenders Squad have descended on a Hamilton wreckers yard.
A witness said "police with dogs and guns pointing at around five people" were at Riverlea Wreckers.
A police spokeswoman said it was a "pre-planned search and AOS is in attendance as a precaution".
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The witness was driving to Cambridge, just south of Hamilton, on State Highway 1 at about 4.45pm when she saw the action.
She said the police were setting up a road block leading to Hamilton as she drove south.
Another motorist said a police car was blocking the on-ramp to SH1 at Tamahere from Airport Rd, preventing northbound traffic getting on to the highway.
Traffic was "horrendous".
A helicopter was circling the area.
Police said there were no arrests.