The six activists spent several hours hanging off the side of the Prirazlomnaya platform in the Pechora Sea attached to the rig's mooring lines. They prepared for a long occupation by bringing up supplies, including the tents, but planned to evacuate after rig workers threw pieces of metal at them.
In a YouTube video posted online by Greenpeace, Terry Christenson, of Parry Sound, Ont., says he's taking part in the action for his grandchildren and "the grandchildren of the planet."
"I think it is a catastrophe waiting to happen," said Christenson, who's been a climber for almost 20 years.
At first, the six activists, who include Greenpeace executive director Kumi Naidoo, were offered hot soup, then were showered with blasts of icy water.
"Not just hosed water, but now metal being thrown by Gazprom crew at our activists," Naidoo said in a tweet, referring to the workers of a subsidiary of Russian energy company Gazprom that owns and operates the rig. "We're coming down."
Two helicopters arrived at the platform, but left without disturbing the protesters. The activists managed to put a banner on the rig saying "Don't kill the Arctic."
"We're here peacefully and we will continue to draw the attention of Russian people and people around the world to what's happening there," Naidoo told The Associated Press by telephone from the platform. "It's bad for Russia, it's bad for the planet."
Gazprom is pioneering Russia's oil drilling in the Arctic. The state-owned company installed the platform there last year and is preparing to drill the first well.
Gazprom said in an emailed statement that the activists "have been invited to scale up to the platform for a constructive dialogue," but said that they refused. The company said that "all work on the platform proceeds as normal."
Naidoo, a South African, said the other activists with him include Christenson, two from Germany, and one each from the United States and Finland.
The platform is about 1,000 kilometres from the nearest port, Murmansk, a city on the extreme northwestern edge of the Russian mainland.
Greenpeace said that its activists have supplies to last "for an extended stay."
Russian and international environmentalists have warned that drilling in the Russian Arctic could have disastrous consequences because of a lack of technology and infrastructure to deal with a possible spill in a remote region known for huge icebergs and severe storms.
An AP investigation last year found that at least one per cent of Russia's annual oil production, or five million tons, is spilled every year.
A report by Greenpeace and World Wildlife Fund, issued last week, said that a spill from Prirazlomnaya could contaminate protected areas and nature reserves on the shore and islands within 20 hours, while emergency teams would take at least three days to reach the area.
_ With files from The Canadian Press.