Eighty-seven people turned up at Christchurch Hospital yesterday after the massacre across two mosques in the city, and three others presented at other community clinics.
Canterbury DHB chief executive David Meates this morning said 20 people were seriously injured.
"At this stage we've got 12 still in ICU - seven in our special surgical care area, one in orthopaedic trauma unit," he said.
"Then we've got a range of the remaining patients in a range of different units and wards throughout Christchurch Hospital.
"Round about 20 of them are at the more serious end."
One of those critically injured is a 4-year-old boy, who has been flown to Auckland's Starship Hospital this morning.
Meates said it was "too early" to comment on whether more patients would die from their injuries, but said there were some "very complex" cases.
He praised the work of the medical staff treating those patients.
"It's a pretty remarkable response, from some pretty remarkable clinical teams."
Meates said the DHB had a "fair bit" of experience responding to large-scale disasters - but said this came as a shock.
"Definitely a shooting of this scale is beyond anything we could have imagined."
About 200 family members of patients were on site yesterday evening, Meates said, many of whom were "very distressed".
Forty-nine people have been confirmed dead in the terrorist shootings, which happened at two Christchurch mosques yesterday afternoon.
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 Ave.
One person died in hospital, after being transported there for their injuries.
Radio New Zealand is reporting the dead include a 5-year-old girl and her father, who were chased by the gunman and shot.
Four people - three men and a woman - were initially arrested after the incident.
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.
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."