Forty-nine people have been killed and at least 20 wounded in shootings at two mosques in Christchurch, New Zealand.
Prime Minister Jacinda Ardern described the incident as a terrorist attack and one of New Zealand's "darkest days".
A man in his late twenties was charged with murder and will appear in court on Saturday morning, police confirmed.
Two other men and one woman were detained nearby and firearms and explosive devices recovered, Police Commissioner Mike Bush said.
He said one of those detained was later released, while officers were working to determine if the other two were involved.
The attack, which came around the time people were attending the mosques for Friday prayers, was the deadliest in the nation's history.
A gunman, who identified himself in footage of an attack as a 28-year-old Australian called Brenton Tarrant, live-streamed his rampage to Facebook from a head-mounted camera. The footage showed him firing indiscriminately at men, women and children from close range inside the Al-Noor mosque.
Police called on the public not to share the "extremely distressing" footage online. Facebook said it had removed the gunman's Facebook and Instagram accounts and was working to remove any copies of the footage.
