A police officer responds following shooting at Linwood in Christchurch, New Zealand, March 15, 2019, in this still image obtained from a social media video. Photo: Reuters.

Wellington - "Let's get this party started" are the opening words in a distressing video circulating online on Friday showing the first of two Christchurch mosque shootings that left at least 49 people dead.

New Zealand police said they were working to have the "footage removed" as they urged people not to share it, while Facebook said that they "quickly removed both the shooter's Facebook and Instagram accounts and the video" after being alerted by police.

Later on Friday New Zealand Prime Minister Jacinda Ardern echoed the police's call, saying that citizens "should not be perpetuating, sharing, giving any oxygen to this act of violence and the message that is sitting behind it."

The video, almost 17 minutes long, shows a white man in camouflage and black clothing driving to what appears to be the Al Noor mosque on Deans Avenue in Christchurch.

There is nationalist Serbian music playing in the car and multiple rapid-fire weapons can be seen in the passenger's seat. The guns have writing on them including one featuring the name "Ebba Akerlund," an 11-year-old girl who was killed in a 2017 terrorist attack in Sweden.

After entering the mosque, the man appears to shoot at least two dozen men in the building as well as at least two people in the street. The video is filmed in the style of a first-person shooter computer game.

He returns to the car to retrieve more weapons and then re-enters the mosque. The video ends with the shooter driving away from the crime scene at full speed and shooting out of the window of his car.

The proliferation of this footage online is dangerous due to the risk of copycat killings, according to Alexander Gillespie, a professor of International Law at University of Waikato.