Armed police have been seen running through the city, where at least six people have been injured.
Police have not confirmed there has been a shooting, but have a advised a “serious incident” has been contained to a building under construction on lower Queen Street.
People are being asked to avoid the area, while people in downtown inner-city buildings are being told to stay inside their buildings.
“This is a significant incident with multiple emergency services responding,” a police spokesperson has advised.
“A large police presence will remain in the area.
“Police will provide a further update as soon as we are in a position to do so.”
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St John Ambulance has said three people have been seriously injured and three people have been “moderately injured”.
Photos of construction workers sheltering on top of a building have been circulating, as has vision of a police officer being ushered into an ambulance with what appears to be injury to his face.
It’s understood the incident began about 7.30am NZST.
New Zealand Prime Minister Chris Hipkins has reportedly cancelled his travel today and is on his way back to the Beehive.
He is expected to speak after being brief by officials on the incident.