PetroChina Co Ltd has started drilling its oil sands field in Canada on Sept 30, a big step in the company's overseas oil sands exploration development, the company said on Monday.

PetroChina International Investment Ltd, a subsidiary of PetroChina, bought a 40 percent stake in the MacKay River oil sands project of Canada's Athabasca Oil Sands Corp in February for C$680 million ($693 million).

Canadian regulators had previously allowed PetroChina to buy 60 percent of the project for C$1.9 billion in November 2011, according to Xinhua News Agency.

The MacKay River oil sands project is located in Alberta province in northwestern Canada, a region that contains 85 percent of the world's oil sands. According to PetroChina, the depth of the oil reservoir is between 160 and 200 meters.