There were dramatic scenes in Mandurah on Sunday evening with officers from the tactical response group (TRG) called to an incident near the CBD.
A man has been taken into custody following the major police response.
Officers were called to the Mandurah Terrace apartments after a witness reported seeing a man with a firearm in the area about 6.30pm.
The man was arrested, but a police spokesman said no firearm had yet been found.
He is understood to be assisting police with their inquiries.
The incident happened near Kingdom City Church, with church proceedings interrupted while officers investigated.
There have been no reports of injuries.
The investigation continues.
