Not less than forty people were killed in a shooting attack on the southern island of New Zealand on Friday when a gunman opened fire inside two mosques.

The shootings in Christchurch, categorized as a terrorist attack, included 30 deaths at one mosque, New Zealand Prime Minister Jacinda Ardern said. Christchurch Hospital also confirmed it was treating 48 people for gunshot wounds, ranging from minor to critical.

The gunman, who was dressed in tactical gear, appeared to live-stream video of the shooting on social media, according to New Zealand police, documenting his trip from his vehicle and into the worship centre in central Christchurch, where he opened fire indiscriminately.

“This is one of New Zealand’s darkest days,” Arden said in a press conference Friday afternoon.

Four people, three men and one woman, were taken into custody in the hours following the attack, but police have not released their identities. Australian Prime Minister Scott Morrison confirmed one of them was an Australian citizen.