New Zealand Prime Minister Jacinda Ardern has addressed the Christchurch shooting amid unconfirmed reports that up to 27 people have been killed.
The Prime Minister's Office confirmed that the National Security System has been initiated, and Ms Ardern will be meeting with the heads of relevant agencies for a meeting at the Parliament's bunker.
The Officials Committee for Domestic and External Security Coordination - commonly referred to as ODESC - is a committee of chief executives which manages national security in New Zealand in both its governance and its response mode.
It's understood members of the group began arriving at the Police National headquarters before 4pm on Friday, ahead of Jacinda Ardern's arrival in Wellington where she is expected to address the nation.
New Zealand Security Intelligence Service (SIS) boss Rebecca Kitteridge was seen heading to the ODESC meeting, along with the heads of the Ministry of Foreign Affairs and Trade (MFTA), Civil Defence, and the Department of the Prime Minister and Cabinet (DPMC).
"Police have one suspect in custody, however there could be others involved," the Prime Minister said on Friday afternoon from Taranaki, where she had been visiting students protesting climate change.
"This is one of New Zealand's darkest days," she continued, adding that her thoughts are "with those in Christchurch".
She called it an "unprecedented act of violence" and said the advice from police "continues to be that people stay indoors".
"This is an act that has absolutely no place in New Zealand - this is not who we are," the Prime Minister said. "They have no place in New Zealand society."
"We are dealing with an evolving situation. Please be assured police are actively managing the situation."
The Prime Minister would not say whether the attacked was on the radar of police or intelligence agencies.
It was confirmed Speaker of the House Trevor Mallard, ACT Party leader David Seymour and National MPs David Carter and Matt Doocey were locked in Canterbury University as part of a delegation speaking to students.
"When we had news of the shooting at the mosque, very soon afterwards the building was locked down we were not allowed to leave and the grounds of the university were cleared," Mallard told Newshub.
National Leader Simon Bridges issued a statement condemning the attacks, saying no one in New Zealand should have to live in fear.