A live video is streamed online showing a gunman driving to a mosque in New Zealand, his car apparently full of weapons and ammunition.
This video - posted live on Facebook - was circulated widely on social media.
The next events mirroring the carnage played out in video games - as the gunman entered the mosque and shot randomly at people inside - before returning to his car and continuing on, shooting out the window.
Shortly before the mass shooting was streamed, an anonymous post online said an attack would take place quote "against the invaders".
A manifesto which denounced immigrants, cited "white genocide" as a motivation - a term used by racist groups to refer to immigration and the growth of minority populations.
The Facebook link directs users to brenton.tarrant.9.
A Twitter handle of a similar name posted pictures of a rifle and military gear decorated with names connected to white nationalism.
Facebook and Twitter say they will take down any content involving the attack - including any praise or support for the crime.
Several people are in custody - one of them confirmed as Australian.
And New Zealand police have charged one man in his late 20s with murder.
He will appear in court on Saturday (March 16).
The New Zealand prime minister described the incident as "terrorism" - and the nation's worst mass shooting in history.