"There was a river of blood coming out of the mosque ... It was literally flowing off terracotta tiles," he said.

"The scene at Deane Avenue was about hatred,"

He and other emergency staff have recalled in detail the scene on Friday after shootings at two mosques left 50 dead and 50 more injured in New Zealand's worst shooting.

Among those on shift when the news broke was a recent graduate from an Australian university on his first day on the job.

"He had spent a total of four weeks in the back of an ambulance prior to that day, so baptism by fire," shift supervisor Jason Watson said.

"He turned up at the mosque and took part."

Some visibly emotional as they grappled with what had occurred, the group of respondenrs told reporters of stepping over bodies to collect the wounded and the unparalleled stream of reports that rushed in from 1.44pm.

Call handler Spencer Dennehy, nine months in the job, discussed how in her first call she had to keep a woman, whose two-year-old and husband were in one of the mosques at the time, from going after her family.

"She was very emotional and hysterical ... she determined to go," Dennehy, a Christchurch resident herself, said, noting all three survived.

"It was very, very distressing ... I was trying to be strong for her."

Watson, meanwhile, said he was left surprised only one victim had died in hospital following the incident.

"A good half of the patients I saw go into the back of ambulances I expected to die within an hour," he said.

"The fact that only one has is incredible and is a plus to the entire Christchurch emergency services community and members of the public that helped out.

Twelve of 50 people injured remained in critical condition over the weekend, including one child.

Australian Associated Press