The gunman who committed the massacres at the Christchurch mosques appears to have narrowly escaped police arriving at the scene by one minute.

Questions have been raised after claims that police and the gunman were at the Al Noor scene at the same time, but police say these claims are wrong "according to the information we have".

The gunman started shooting at about 1.40pm and spent about six minutes at Al Noor Mosque on Deans Ave before driving off towards Linwood Islamic Centre, according to reports describing the gunman's livestreaming video, which has since been classed as objectionable.

He departed Al Noor Mosque at about 1.46pm on March 15. Police say the first armed police unit arrived on the scene at 1.47pm.

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Act leader David Seymour said two people had told him that police were at the Al Noor Mosque at the same time as the gunman, but he was quick to add that they could be mistaken.

"One of them has subsequently said they won't stand by it because they're not sure. The other one is confident that what they told me is correct. Their understanding is that the first police arrived before the offender departed," Seymour said.

He added that police also needed to answer questions about why they couldn't stop the gunman before he arrived at Linwood Islamic Centre and opened fire again.

"How is it possible that someone can commit one atrocity, drive 7km across a major city and commit another one? It's extraordinary," Seymour said.

"I don't think there's been a terrorist attack in the world where the terrorist moved to multiple sites."

The Pakistani community, who lost three people in the Linwood Islamic Centre, have raised the same question.

Seymour called for the police response to be included in the Royal Commission of Inquiry, but the Government has said the review of first responders would be done separately.

Police declined to detail their response to the shooting at Linwood Islamic Centre, or whether there was an opportunity to intercept the gunman on his way to Linwood.

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A spokeswoman said police just missed the gunman fleeing Al Noor Mosque.

"Our information shows the offender had left, narrowly missing our arriving officers."

Police Commissioner Mike Bush said the response was as quick as "humanly possible to an unprecedented, highly planned and rapidly unfolding event".

"In due course we will release a detailed timeline of the response which will show second by second exactly how police responded. In the meantime I reiterate that the offender was apprehended 21 minutes after we received the first emergency call."

Prime Minister Jacinda Ardern also said there would be a review into the first responders, but the focus for now was to allow police to complete its investigation.

She added that she was yet to take advice on the nature of that review, but it would not be part of the Royal Commission of Inquiry.

The information released by police showed that the alleged gunman was apprehended in a "very short time period".

"At the time they were deployed, they didn't necessarily have the detail required to be able to track the movements of the offender, but regardless of that still managed to detain the [alleged] offender within a pretty quick timeline," Ardern said.

St John Assistant Director of Operations Doug Gallagher said the first 111 calls for ambulance services came in at 1.44pm, and the first ambulance was dispatched at 1.51pm.

"Our emergency call handlers received 28 calls for an ambulance during the Christchurch incident. These include 18 for Deans Avenue, eight for Linwood Ave and two for other addresses where it appears patients had escaped to.

"Six calls were answered by our call handlers in Auckland; 10 in Wellington; and 12 in Christchurch."

St John dispatched 12 ambulances and two managers to the Deans Ave site. and six ambulances were dispatched to Linwood Ave and the two other addresses.

March 15 timeline

1.30pm:

Friday prayers begin at Al Noor Mosque and Linwood Islamic Centre

1.33pm: Gunman starts streaming FB live video. Drives a few blocks to Al Noor mosque

1.40pm: Gunman arrives at Al Noor Mosque and starts firing

1.41pm: First 111 calls to police

1.43pm: Gunman returns to his car for more weaponry, then returns to mosque

1.44pm: First 111 call to St John ambulance services

1.46pm: Gunman departs Al Noor mosque and heads to Linwood Islamic Centre, 7.3km away

1.47pm: First armed police unit arrives at Al Noor Mosque

1.49pm: Facebook livestream cuts out while gunman is driving to Linwood Islamic Centre

1.51pm: First Armed Offenders Squad arrives at Al Noor Mosque; first ambulance dispatched to Al Noor Mosque

1.55pm: Gunman enters Linwood Islamic Centre

1.57pm: First 111 St John Ambulance call from Linwood Islamic Centre

2.02pm: Suspected gunman is apprehended by two police officers on Brougham St, about 5km to 6km from Linwood Islamic Centre

2.16pm: Suspect is in custody at the Christchurch Justice Precinct