The shootings took place at the Al Noor Mosque and Linwood Masjid, The New Zealand Herald reported.

One gunman, believed to be Australian, filmed as he shot victims in the mosque - and wrote a manifesto declaring his intentions, saying that "it is a terrorist attack", Police Commissioner Mike Bush said.

He said there were also multiple improvised explosive devices attached to vehicles as part of the attack.

"This goes to the seriousness of the situation," Bush said.

The Bangladesh cricket team now touring New Zealand had a narrow escape as the entire team had gone to one of the mosques near Hagley Park for Friday prayers.

Player Tamim Iqbal tweeted that the "entire team got saved from active shooters".

Bangladesh Cricket Board spokesman Jalal Yunus said most of the team had gone to the mosque by bus and were about to go inside when the incident took place.

Authorities immediately called off the New Zealand-Bangladesh third Test match that was set to be played in Christchurch.

Prime Minister Ardern confirmed the fatalities and described the killings as "extreme and unprecedented violence". Police reported that four people -- three men and a woman -- had been arrested for the killings.

"We are not aware of other people but we cannot assume there are not others at large," Bush told the media here.

The government advised people not to go to mosques until further notice. All Christchurch schools were hurriedly shut down.

One man, Robert Weatherhead, told Newstalk that he took in people who escaped from the Al Noor mosque.

He described the gunman as "white, aged in his 30s or 40s and wearing a uniform", but he could not make out what the uniform was.

Another witness, who was in the front row of devotees when the gunman came in, told The New Zealand Herald that the suspect first shot people outside, adding that he heard the gun being reloaded about three times.

"The gunman began shooting in all directions," the witness said.

A woman told the Christchurch Star she lay in her car near the mosque as four to five men came running towards her.