The mayor of Christchurch, Lianne Dalziel, is urging the people of Christchurch to stay inside as she reacts to the "shocking incident".
"It's a dreadful day, this has been an incredibly shocking incident," she told Magic Talk.
"I would never have expected anything like this to happen in the city of Christchurch. I would never expect anything like this to happen to New Zealand."
She is currently in lockdown inside the council building.
Dalziel had been in Cathedral Square to receive an open letter from the students protesting, some of whom are now with her and other staff.
"We're looking after some of the students who were on the climate rally today. They are safe here. We will keep them here until police say they can leave."
She is urging people to stay calm and reiterated an urgent message from police to stay away from the central city, adding that if anyone is inside a building to stay there, as it is safer.
Dalziel is working with police who have briefed her once but expects another update soon.
All the council buildings are in lockdown and police are requesting all central building owners stay away from the city.
Police have confirmed a serious firearms incident close to the central city.
"They are having another briefing at the moment so I am hoping to get an update soon."
She said officers are treating it "very seriously" and actively working to get the matter under control.