Six activists from environmental group Greenpeace scaled a crane at the construction site of a coal-fired power plant in South Africa on Monday and unfurled banners calling it a "climate killer".

The group criticised South Africa, which hosts UN climate talks at the end of the month, for failing to break its heavy reliance on coal-fired power, currently more than 90 percent of state utility Eskom's electricity supply.

"Greenpeace Africa is calling on Eskom to stop its coal addiction and instead invest in large-scale renewable energy projects," the organisation said in a statement.

The activists occupied the 150-metre (492-foot) crane at the Kusile power station in the northeastern province of Mpumalanga for more than five hours before being arrested, Greenpeace said.

Eskom said there was no damage to the site and construction was not interrupted.

Police said they arrested nine activists in all.

The stunt came three weeks before South Africa hosts UN climate talks seen as a make-or-break chance to continue the Kyoto Protocol, the only deal to date with binding targets to cut greenhouse gas emissions.

South Africa has committed itself to slashing coal to 65 percent of the energy mix by 2030, investing heavily in nuclear and renewable energy to make up the difference.

But the country has come in for criticism for going ahead with construction of Kusile and another coal-fired plant, Medupi. Both stations will have a capacity of 4,800 megawatts, making them two of the world's largest coal-fired plants.