China has emerged as the top customer for Canadian oil shipped on the expanded Trans Mountain Pipeline, ship tracking data shows, as a U.S. trade war has shifted crude flows in the year since the pipeline started operating.

China’s new interest in Canadian oil comes as U.S. President Donald Trump’s trade war has strained relations between longtime allies Washington and Ottawa. It also reflects the impact of U.S. sanctions on crude from countries like Russia and Venezuela.

Canada is the world’s fourth-largest oil producer, but its main oil-producing province of Alberta is landlocked with limited access to tidewater ports. That means the bulk of Canadian oil — about four million barrels per day or 90 per cent — is exported to the U.S. via pipelines that run north-south.