Christchurch Hospital staff were "horrified, stunned and angered" by the mosque shootings that killed 50 people, says its head of surgery.

Greg Robertson told reporters this afternoon that after Friday's shootings staff had to triage and deal with life-threatening patients first.

"We do the minimum as trying to preserve as much as possible, then go back and do further surgery later on," Robertson said.

After lesser injuries, they were dealing with things like infections.

"There are two ... children in [Christchurch] hospital at the moment. They are both stable," he said.

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Another child was in Starship in Auckland.

"It's a bit challenging for people ... we are struggling with it as much as anybody else," Robertson said.

"This is not something we expect to see in our environment ... we see gunshot wounds, but 40 to 50 in one day is not what we expect."

"Dealing with 50 people in a day is more than what we should see, so our staff are doing remarkably well."

Most people cope pretty well but it's when they go home that they start to think about it, he said.

Staff were "horrified, stunned and angered", he said.

He spoke about the impact of having gone through the Christchurch earthquakes, and how the experienced staff have dealt with trauma.

"We have been there."

"We only had one death in a patient that arrived at the hospital. Those who got there have a chance. Those who didn't get here didn't have a chance."