Multiple people have been killed after gunman opened fire at two mosques in the New Zealand city of Christchurch.

A gunman opened fire on two mosques in New Zealand on Friday, killing multiple people in what the country’s prime minister called ‘an extraordinary and unprecedented act of violence.’

The shootings in the city of Christchurch were apparently streamed on Facebook, a grim development in terrorism that raised questions about the ability of tech companies to block violent content, reports nytimes.com.

The police said three men and one woman were in custody, but they were unsure if there were others involved.

Shortly before the shooting, someone appearing to be the gunman publicly posted links to a manifesto on Twitter and 8chan, an online forum. The 8chan post included a link to what appeared to be the gunman’s Facebook page, where he said he would soon broadcast live video of the attack.

The man who claimed responsibility for the shootings left a 74-page anti-immigrant manifesto in which he explained who he was and his reasoning for his actions. He said he considered it a terrorist attack.

The 17-minute video, which appeared to be recorded on a helmet camera, shows his drive to the mosque, followed by a harrowing nearly two minutes of his firing on the worshipers in the mosque before fleeing the building and running back to his car and swapping weapons.

He then is seen re-entering the mosque and again begins shooting, continuing to methodically move through the mosque. Several victims can be seen in the footage, many laying on top of one another motionless in a corner of the room.

After another few minutes, he leaves again, gets in his vehicle and drives away, talking to himself throughout.

‘There wasn’t even time to aim, there was so many targets,’ he says at one point.

The video and Twitter posts showed weapons covered in the names of past military generals and men who have recently carried out mass shootings.

In his manifesto, he identified himself as a 28-year-old man born in Australia. He listed his white nationalist heroes, described what he said motivated him to attack, and said he purposely used guns to stir discord in the United States around the Second Amendment.

The shooting happened a day after the country’s minister for climate change, James Shaw, 45, told the police that he was grabbed and hit on the street in the country’s capital, Wellington.

Reports of the shooting happened as young protesters were gathering in Christchurch and cities around the world to demand action on climate change.

Christchurch, with about 388,000 residents, is the biggest city on New Zealand’s South Island, hugging the Pacific Ocean coast.

There hasn’t been a mass shooting in New Zealand since 1990, when a man killed 13 people, including two 6-year-olds, after a dispute with his neighbor in the seaside town of Aramoana.

That shooting led to tightened gun laws, including restrictions on ‘military style semiautomatic weapons.’

Gun owners must be licensed, a process that includes a review of criminal activity and mental health, attendance at a safety program, an explanation of how the gun would be used, a residence visit to ensure secure storage, and testimonials from relatives and friends.

Murders are rare in New Zealand, and gun deaths even rarer. There were 35 murders countrywide in 2017. Since 2007, gun homicides have been in the single digits each year except 2009, when there were 11.

But there are plenty of guns. There were 1.2 million registered firearms in a country of 4.6 million people in 2017, according to the Small Arms Survey, a Swiss nonprofit.