New Zealand Prime Minister Jacinda Ardern’s office has confirmed it received a copy of the alleged Christchurch mosque shooter’s “manifesto” minutes before the attack.

A spokesman for Ms Ardern told New Zealand media that the document was sent to a generic address not checked by the Prime Minister, as part of a bulk email that also went to about 70 people and organisations worldwide, including New Zealand political figures and domestic and international media organisations, The New Zealand Herald reported.

The message, received less than 10 minutes before the attack on Friday, did not set out what was about to happen, and was immediately sent to security and the police, he said.

“The mail was setting his reasons for doing it,” the spokesman told The Herald. “He didn’t say this is what I am about to do. There was no opportunity to stop it.”

Fifty people have been confirmed dead in the terrorist attack, and 39 people remain in hospital, 11 in intensive care.

The man charged with murder over the attack, Brenton Tarrant, 28, from Grafton in NSW, had posted a 74-page document online before the attack, saying he hoped to create fear.

A grim Police Commissioner Mike Bush briefs reporters on the “complex” investigation’s progress. Photo: ABC

Police have been piecing together what’s been described as a “complex event”, following the shocking shooting spree.

New Zealand Police Commissioner Mike Bush on Sunday told reporters four other people arrested during Friday’s police operation attack have either been released or charged with “tangential” offences.

A man and a woman were held in custody while police investigated their involvement, if any, in the two shooting attacks. Mr Bush said the woman had been released without charge.

“The man in the vehicle has been charged with firearms offences. At this point, we do not believe that they were involved in these attacks,” Mr Bush.

A third man – aged 18 – has also been charged, but is not believed to have been directly involved in the attacks.

Meanwhile, the PM revealed on Saturday that Tarrant had intended to carry on his murderous crusade beyond the massacres at the two mosques.

“The offender was mobile. There were two other firearms in the vehicle the offender was in,” Ms Ardern said.

It was absolutely was his intention to continue with his attack … [The officers] put New Zealand first.”

The PM was also forced to defend the response time of emergency services, which has been questioned by some of the worshippers at the mosque on Deans Avenue, where 42 people were killed.

Tarrant was apprehended 36 minutes after the first call to police, Ms Ardern said.

“Police responded immediately to the call they received relating to the attack.”

Tarrant was not on any terror watch list in New Zealand or Australia, it was also revealed.

Tarrant did white power salute

Handcuffed and wearing a prison robe, Tarrant appeared calm during a three-minute appearance, gazing around a packed courtroom in Christchurch on Saturday morning.

As he was being brought into court he made a white power gesture, media reported.

Tarrant was charged with one count of murder, entered no plea and will be required to appear again on April 5. Further charges are expected to be laid.

Tarrant did not apply for bail, nor to have his name suppressed, and has been remanded in custody.

Two other people in custody are yet to be charged, but Ms Ardern said inquiries were ongoing to establish whether the other two were directly involved.

Many still critical

Almost a dozen shooting victims, including two boys, had surgeries after the attacks on Friday after doctors from across New Zealand headed to Christchurch.

Christchurch Hospital’s chief of surgery Greg Robertson spoke to reporters on Saturday, revealing the youngest victim to survive the shooting spree was aged just two years old. The other boy was 13.

Both are in a stable condition.

Dr Robertson said 12 operating theatres worked overnight at the city’s main teaching hospital, where 11 patients remain critical in the intensive care unit, one of them a woman in her 20s.

“Of the 48 patients admitted to Christchurch Hospital from the incident, seven have been discharged. The others include a four-year-old girl ,who has been transferred to Auckland’s Starship Hospital in a critical condition.

“Four patients died on their way into the hospital yesterday, dying before they arrived.”

A total of 39 patients remain in hospital.

There are grave fears the death toll may rise. It currently stands at 50 dead.

“They [the injuries] range from soft-tissue injuries to more complex injuries involving the chest, abdomen, pelvis, long bones and the head. Many of the people will require multiple trips to theatre to deal with the complex series of injuries that they have,” Dr Robertson said.

-with AAP