At least 40 people have been killed after shootings at two mosques in the New Zealand city of Christchurch.
Three men and one woman are in custody, but police have warned there could be other attackers at large.
One of the arrested suspects is Australian, Australian prime minister Scott Morrison confirmed.
Footage on social media appeared to show a gunman live-streaming as he entered a mosque with his weapon drawn
40 people killed across two locations, more injuries
Three men and one woman are in custody
Police have defused multiple IEDs found on vehicles
Shooter reportedly live streamed video of attack
Bangladesh cricket team escaped from mosque attack
Jacinda Ardern: this is “one of New Zealand’s darkest days”
Everything we know so far about the Christchurch attacks
Forty people have been killed and more than more 20 seriously injured at two mosques in the New Zealand city of Christchurch after at least one gunman opened fire on worshipers.
Witnesses told media that a man dressed in a military-style, camouflage outfit, and carrying an automatic rifle had started randomly shooting people in the Al Noor mosque shortly after 1.40pm local time (12.40am GMT).
Video footage widely circulated on social media, apparently taken by a gunman and posted online live as the attack unfolded, showed him driving to one mosque, entering it and shooting randomly at people inside.
New Zealand Police Commissioner Mike Bush said police had also defused a number of improvised explosive devices found on vehicles after the mosque shootings.
Mr Bush confirmed police now have four suspects in custody – three men and one woman with one confirmed to be an Australian citizen. New Zealand’s Prime Minister said the suspects held extremist views, but had not been on any police watchlists.
Mr Bush warned it was not possible to assume that the attack was isolated to Christchurch, saying: “At this point in time we should never make assumptions.”
New Zealand had been placed on its highest security threat level.