Wellington's The Terrace was closed as several fire trucks and a HAZMAT unit respond to "an incident" near the Treasury building.
The fire service says it was called around 6pm on Monday to investigate the smell of smoke.
By 7pm, it said the operation was being scaled down, with the street reopened shortly therafter.
Police have told Newshub they are in attendance, but only for traffic control.
Metlink has advised bus travellers to expect delays.