Young children are among the dead and injured in a massacre across two Christchurch mosques, which has been classed a terrorist attack by the Prime Minister.

Forty-nine people have died and 42 of the 48 injured are being treated in hospital.

Two patients are critically injured - including a 4-year-old child, who is being transferred to Starship Hospital this morning.

Radio New Zealand is reporting the dead include a 5-year-old girl and her father, who were chased by the gunman and shot.

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There is a possibility the death toll could rise, as some patients in Christchurch hospital are critically injured.

A statement by Police Commissioner Mike Bush issued this morning confirmed 41 people were killed at a mosque on Deans Ave, near Hagley Park.

Seven others were killed at a second mosque, on Linwood Avenue.

One person died in hospital, after being transported there for their injuries.

Four people - three men and a woman - were initially arrested after the incident.

Ambulance staff take a man from outside a mosque in central Christchurch, New Zealand. Photo / AP, Mark Baker
Ambulance staff take a man from outside a mosque in central Christchurch, New Zealand. Photo / AP, Mark Baker

A 28-year-old man is due to appear in Christchurch District Court this morning, facing a murder charge.

The main shooter has been identified by Australian police as Brenton Tarrant — a white, 28-year-old Australian-born man, who uploaded to his Twitter account before the shooting a manifesto explaining his intentions.

Two of the three other people apprehended yesterday remain in custody.

The fourth person was found armed at the scene but didn't appear to have had anything to do with the killings.

Police were still "working to understand" what involvement the other two, who were also armed, had in the shootings.

A large police presence remains in Christchurch, and a heightened police presence can be expected at community events nationwide for safety and reassurance.

Dozens more officers will be sent into the region today, and the Police Eagle Helicopter has been deployed to Christchurch to assist with inquiries on the ground.

Wally Haumaha, the Deputy Commissioner of Maori and Ethnic Services, has travelled to Christchurch with 15 ethnic liaison officers.

"These specialists will work alongside local staff to support the families and help repatriate them with their loved ones in a way that is consistent with Muslim beliefs, while taking into account these circumstances and obligations to the coroner," Bush said.

"I also plan to fly to Christchurch this morning, and will be speaking to media at the earliest opportunity."

An armed policeman is patrolling the area outside the Christchurch District Court, where the murder accused is due to appear after 9am.

The courthouse is in a justice precinct next to the police station.

Media from around the world are gathering outside the building.

Bush said officers had disarmed two improvised explosive devices found in a vehicle used by those believed to be behind the attack.

Speaking to media at Parliament last night, Ardern described the attack as "an act of terror".

She said New Zealand represents kindness, compassion and a home for those who share New Zealand's values.

"Those values, I can assure you will not and cannot be shaken by this attack."

Speaking directly to the killers, Ardern said: "You may have chosen us, but we completely reject and condemn you."