Christchurch terror attack: Shock suspects weren't on watchlists

A former police negotiator has been trying to piece together how none of the alleged perpetrators of Friday's Christchurch terror attack were on intelligence agencies' watchlists.

Forty-nine have so far been confirmed killed in by far New Zealand's deadliest-ever shootings, which took place at two mosques in the South Island's biggest city. Dozens more remain in hospital.

Four suspects are in custody, one of them expected to appear in court later on Saturday.

Former police negotiator Lance Burdett says unlike known gangs, they flew under the radar.

"It's closed groups - they know each other, they would maybe have grown up with each other... more so than a criminal gang," he told Newshub.

"New Zealand's quite a small place. To get something like this underway and to keep it quiet, particularly with the number of people involved, surprises me."

Burdett says this attack on home turf is unprecedented.

"New Zealand police are trained for this type of thing. I often say 'expect the unexpected' with the likelihood of things happening like this, it's not going to happen. And here it is - it's happened."

The previous worst shooting massacre in New Zealand history took place at Aramoana in 1990, where 14 lost their lives, including gunman David Gray.

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