(CNN) Canadian Prime Minister Justin Trudeau was greeted in London on Wednesday with a 98-foot fake pipeline meant to challenge his support of a controversial oil pipeline in his country.

The stunt, which blocked the main entrance to the Canadian High Commission, was orchestrated by Greenpeace activists who oppose a multibillion-dollar pipeline planned in western Canada across indigenous lands.

The Trans Mountain expansion, approved in 2016, will help oil companies reach new markets by expanding the capacity of North America's only pipeline with access to the West Coast, and it will nearly triple the number of oil tankers traveling the shared waters between Canada and Washington state.

Police stand guard as Greenpeace activists build an "oil pipeline" outside Canada House.

Greenpeace activists said the project will take highly polluting tar sands to global markets, and that building the pipeline would make Trudeau's claims of climate leadership a "laughingstock."

"Trudeau is risking the health of Canada's rivers and coast, the water supply and livelihoods of many indigenous people, and undermining the credibility of the Paris climate agreement, all to keep some struggling oil companies in profit," Greenpeace UK oil campaigner Sara Ayech said in a news release.

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