No nation is more thirsty for Canadian oil than China. But until now, the oil from Alberta has only flowed south to the United States.

Now the Canadian Government has approved a proposal for a major pipeline to transport the country's oil to Asia, despite powerful resistance from environmental groups, the First Nations and Prime Minister Stephen Harper's political rivals in Parliament.

Canada's Alberta province has 170 billion barrels of proven oil reserves, a resource surpassed only by Venezuela and Saudi Arabia. The Calgary-based energy company, Enbridge, now plans to build a 1175km pipeline from the tar sands town of Brudherheim across British Columbia to the Pacific coast, where it would generate 525,000 barrels of oil a day for export to Asia.

China, whose state-owned companies have recently invested more than US$40 billion ($45.89 billion) in Canadian energy, is in line to benefit from the pipeline. Its supporters claim it will boost the Canadian economy, creating jobs and adding an estimated US$300 billion to Canada's GDP over the next 30 years.

As much as 97 per cent of Canada's oil exports are to the US, and many consider the proposed US$7 billion project a crucial diversification. However, the Northern Gateway pipeline would pass through large swathes of land owned by native tribes and the pristine Great Bear Rainforest.

And, when it arrives at the port of Kitimat, environmental activists fear the possibility of pipeline leaks or a tanker spill. More than 200 large oil tankers a year would sail in and out of Kitimat and the region still remembers the devastating Exxon Valdez oil spill of 1989, which continues to affect local ecosystems 25 years later.

The Northern Gateway project was first proposed in 2006 and has been delayed several times because of heated opposition. Harper claims the pipeline is essential to Canada's national interest, especially since April, when the Obama Administration indefinitely postponed approval of the Keystone XL pipeline, which would transport Alberta oil through the US to the Gulf Coast in Texas. Harper was "profoundly disappointed" by the decision.

Canadian regulators have drafted a list of 209 conditions, which the Government says Enbridge must satisfy before construction can begin.

"In addition, consultations with aboriginal communities are required," Natural Resources Minister Greg Rickford said. "[Enbridge] clearly has more work to do in order to fulfil the public commitment it has made to engage with aboriginal groups and local communities along the route."

Enbridge has suggested it may take as long as 16 months to meet the regulator's conditions. Its president, Al Monaco, said said while the economic arguments for the pipeline are clear, the public still wants reassurance that the project is environmentally sound. "If we can't prove our safety and environmental protection, the economic benefits won't matter. In other words, the economic benefits alone are not enough to sustain public support."

The opposition is fiercest in British Columbia, where Premier Christy Clark has set five conditions for the support of the provincial Government, including "world-leading" infrastructure for preventing and responding to land or marine oil spills, and an assurance that British Columbia will receive a "fair share" of the economic benefits from the project.

Clark, whose Administration can deny construction permits, says those conditions are yet to be met.

On Wednesday hundreds poured on to the streets of Vancouver to protest against the Government's decision. Environmental groups have insisted the Ottawa Government's approval does not guarantee the project will go ahead, while more than 130 First Nations have now signed a declaration banning the Northern Gateway pipeline from crossing their territories. "I never want to dip my paddle in oil," Bryan Joe, a member of the Comeakin Nation, told a hearing last year.

Though Canada's Supreme Court has ruled in the past that native groups must be consulted on any construction project that encroaches on their land, legal experts say their powers do not include a veto. Nevertheless, Stewart Phillip, the Union of British Columbia Indian Chiefs Grand Chief Steward, said the region's indigenous tribes would block any attempts by Enbridge to begin building. A coalition of the region's native groups promised to "defend our territories whatever the costs may be".

Tom Mulcair, the leader of the opposition New Democratic Party, and the leader of the Liberal Party, Justin Trudeau, both said they would reverse the decision to approve the pipeline were they to take power at the next Canadian general election in October 2015.

Northern Gateway

•US$7b project

•170b barrels of oil reserves in Alberta

•1175km pipeline from Brudherheim to the Pacific coast

•US$300b to Canada's GDP over the next 30 years

- Independent