Gunmen have opened fire at mosques in Christchurch, with reports of between nine and 27 people killed and police urging residents to stay indoors.

One man is in custody.

Prime Minister Jacinda Ardern called it "one of New Zealand's darkest days".

One of the gunmen broadcast live as he shot victims.

Ardern described the event as "extreme and unprecedented violence".

Police were "actively managing the situation" and confirmed multiple fatalities.

The multiple fatalities were at two locations - a mosque at Deans Ave and one at Linwood Ave.