Canadian farmers produced the smallest canola crop in four years, less than expected, after unusually wet autumn weather that left millions of acres unharvested, a government report showed on Friday.

Farmers produced 18.6 million tonnes of canola, down 8% from last year, Statistics Canada reported, and 1 million tonnes less than the average trade guess before the report. Canada is the world's biggest canola producer and exporter.

Statistics Canada's production report was based on a survey of farmers that asked them how much of each crop they harvested or intended to harvest. With more than 2 million acres of canola alone left in frozen fields, the question was open to farmers' interpretation this year, analysts said.

"It was a tough guess. You don't know how growers are going to respond with so much canola under two feet of snow," said Ken Ball, senior commodity futures advisor at PI Financial Corp.

Farmers' canola crop disappointed in a year in which China has sharply reduced its imports from Canada in a broad diplomatic dispute involving the arrest of a Chinese Huawei Technologies Co executive. Demand from domestic crushers that process canola for its vegetable oil and meal, such as Bunge Ltd and Cargill Ltd, has been strong.