Watch: 6000 Danish heavy metal fans perform spine-tingling haka for Kiwi band

More than 6000 heavy metal fans have gone viral after they performed a spine-tingling haka alongside New Zealand te reo thrash metal band Alien Weaponry at a music festival in Denmark over the weekend.

The Northland-based band took to the stage at the Copenhell festival in Copenhagen and opened the show with a traditional haka, a performance they like to do at the beginning of every show.

Before starting, the band welcomed Kane Harnett-Mutu on stage, a Kiwi who has been teaching the haka in Denmark for more than 20 years.

As the three-piece band finished their welcome, they were left stunned when the 6000-strong crowd and Harnett-Mutu responded to the group with their own haka.

Copenhell's communications chief, Morten Skovgaard, requested the crowd respond to the band as a way to "express their respect for both the band and Māori culture".

In a video posted on the festival's social media pages, organisers say "two different cultures met in a shared, emotional and powerful experience".

"More than 6000 metalheads yesterday, New Zealand Alien Weaponry welcomed Copenhell with the craziest haka greeting the band has ever experienced," the festival organisers wrote.

Harnett-Mutu also took to social media to thank the crowd for their amazing performance and said he was honoured to be given the opportunity to organise a 6000-strong haka.

"The crowd were so energised and incredibly respectful. They opened their arms and embraced their haka and through it... A deeper connection to Te Ao Māori and the band.

"An honour to tautoko your mahi, boys and to be part of this fantastic experience."

After the haka, drummer Henry de Jong told the camera: "I loved it, you guys did so well. The whole show, you guys were amazing.

"I don't think we've had a haka that size at one of our shows... to have a few-thousand people doing it is absolutely mind-blowing."

Alien Weaponry are well-known for their fusion of te reo Māori with thrash metal. The Northland group are currently on a world tour playing festivals such as Hellfest and MetalDays.