A horrific shooting at a Christchurch mosque was livestreamed for 17 minutes by the gunman.
Australian police have identified the shooter as Brenton Tarrant - a white, 28-year-old Australian-born man. Twitter has shut down a user account in that name.
The gunman published an online link to a lengthy "manifesto", which the Herald has chosen not to report.
Police Commissioner Mike Bush said he was aware that footage of the shooting was on social media and police were doing everything they could to get it removed.
"It shouldn't be in the public domain."
Facebook Australia-New Zealand policy director Mia Garlick said videos which appeared to show the Christchurch shootings had been taken down.
"New Zealand Police alerted us to a video on Facebook shortly after the livestream commenced and we quickly removed both the shooter's Facebook and Instagram accounts and the video."
Spark managing director Simon Moutter said the company was working to close off websites attempting to distribute the footage.
Vodafone NZ spokesman Richard Llewellyn said: "Industry players are working at a technical level now to block some of the hate sites involved in this content."
Spark spokesman Andrew Pirie said technical staff had identified three primary sites where footage had been posted but there were a number of "copycat" sites popping up.
The internet providers had joined forces to block access to these sites, he said.
Australian media have reported that New South Wales counter-terrorism police were carrying out activities in the Coffs Harbour area of New South Wales.
It was not known whether "Tarrant" was from Coffs Harbour but he was certainly from NSW, Nine News Sydney reported.
Our Spark security experts are working hard to close off the websites attempting to distribute the hateful stuff originating from the perpetrators of the massacre in Christchurch. We hope it causes minimal inconvenience to legitimate internet use by our customers.— Simon Moutter (@simonmoutter) March 15, 2019
It's believed the man may have family in Grafton, northeast of Coffs Harbour.
The 17-minute livestream began as the gunman drove to the Al Noor Mosque in Deans Ave.
His beige station wagon contains a cache of weapons and ammunition in the front passenger seat and boot, along with petrol canisters.
Filmed on a helmet camera it shows the gunman walking in to mosque front door and opening fire. He is inside for three minutes, returns to his vehicle to get more ammunition and then re-enters the mosque and opens fire again.
The 17-minute video ends as the gunman drives away at speed.