Prime Minister Jacinda Ardern has described today's shooting in Christchurch as a "terrorist attack".

'I have now had the opportunity to be fully briefed with the details of the unprecedented events that took place in Christchurch this afternoon."

Addressing the nation from the Beehive tonight, Jacinda says "it is with extreme sadness that I tell you that as at 7pm tonight, we believe that 40 people have lost their lives in this act of extreme violence.

"10 have died at Linwood Avenue Mosque, 3 of which were outside the mosque itself."

A further 30 have been killed at Deans Avenue Mosque.

There are also more than 20 seriously injured who are currently in Christchurch A&E.

"It is clear that this can only be described as a terrorist attack," says Jacinda.

"From what we know, it does appear to have been well planned. Two explosive devices attached to suspects' vehicles have been found and they have been disarmed.

"There are currently four individuals who have been apprehended but three are connected to this attack and are currently in custody, one of which has publicly stated that they were Australian born.

"These are people who I would describe as having extremist views that have absolutely no place in New Zealand and in fact have no place in the world.

"While we do not have any reason to believe at this stage that there are other suspects, we are not assuming that at this stage. The joint intelligence group has been deployed and police are putting all of their resources into this situation," says Jacinda.

"The defence force are currently transporting additional police staff to the region.

"Our national security threat level has been lifted from low, to high. This I want to assure people is to ensure that all our agencies are responding in the most appropriate way. That includes at our borders.

"Air New Zealand has cancelled all turbo prop flights out of Christchurch tonight and will review the situation in the morning. Jet services both domestically and internationally are continuing to operate.

"There is heightened security, so we can assure people of their safety and the police are working hard to ensure people are able to move around their city safely.

"I have spoken this evening to the mayor of Christchurch and I intend to speak this evening to the imam, but I also want to send a message to those directly affected.

"In fact, I am sure right now New Zealand would like me to share a message on their behalf too.

"Our thoughts and our prayers are with those who have been impacted today. Christchurch was their home. For many, this may not have been the place they were born, in fact for many, New Zealand was their choice.

"The place they actively came to, and committed to. The place they were raising their families. Where they were parts of communities that they loved and who loved them in return. It was a place that many came to for its safety. A place where they were free to practice their culture and their religion," says Jacinda.

"For those of you who are watching at home tonight, and questioning how this could have happened here.

"We, New Zealand, we were not a target because we are a safe harbour for those who hate.

"We were not chosen for this act of violence because we condone racism, because we are an enclave for extremism.

"We were chosen for the very fact that we are none of those things.

"Because we represent diversity, kindness, compassion. A home for those who share our values. Refuge for those who needs it. And those values will not and cannot be shaken by this attack.

"We are a proud nation of more than 200 ethnicities, 160 languages. And amongst that diversity we share common values. And the one that we place the currency on right now is our compassion and support for the community of those directly affected by this tragedy.

"And secondly, the strongest possible condemnation of the ideology of the people who did this.

"You may have chosen us – we utterly reject and condemn you."