A fake iceberg anchored in Wellington Harbour was driven by a desire to shock people into action on climate change, the group behind it says.

The iceberg was made by special-effects company Weta Workshop for the protest.

Measuring 7 metres long, 3.5m wide and 4.8m high, it is made from polystyrene but fully encased in a hard shell, with a flotation device. It was anchored in Oriental Bay early yesterday.

A group of self-described anonymous artists claimed responsibility for the iceberg via email, saying global warming was a defining topic of our time.

They said they were not affiliated to any group but were just "people who care, people who have children". "We are a collective of artists from all walks of life. "

"We wanted to shock people out of their numbness and hopefully motivate some action. So from that the iceberg was born."

They appealed to people who saw the artwork to "stand up and take action".

"We didn't just talk, we did something. What are you going to do?" they wrote in an email.

The iceberg was trucked through Wellington at night and dropped into the harbour just after midnight yesterday.

"It was a huge relief to see it floating; due to its size, sea tests weren't possible beforehand."

Weta Workshop spokeswoman Ri Streeter said it was commissioned by the artists, who wanted to create awareness of global warming. Weta worked with the group to ensure the artwork was "environmentally sound".

Maritime police spokesman Andrew Cox said there was no problem with the iceberg as it was away from shipping lanes.