China says 'pests' found in blocked Canadian canola shipments

China's removal of the export permit of a major Canadian canola company followed the discovery of "hazardous pests" in shipments, the foreign ministry said Wednesday in a move that has stoked diplomatic tensions.

Canada's largest agricultural handler, Winnipeg-based Richardson International, had its licence to ship canola to China revoked on March 1, which risks leaving Canadian farmers with a glut on their hands.

"Chinese customs recently detected dangerous pests in canola seeds imported from Canada," Chinese foreign ministry spokesman Lu Kang told a regular briefing.

"Canola seeds exported from one company had particularly serious issues leading to (stocks being) quarantined," he said.

Lu said the decision to suspend imports was taken to minimise the "serious threat to agriculture and ecology" from harmful pests and was "completely reasonable and legal".

"Like any other country, the Chinese government also needs to protect the health and safety of its own citizens," he added.

Canada exported more than Can$5 billion (US$3.75 billion) worth of canola last year, with almost half of it, or about five million tonnes, going to China, according to industry figures.

Canadian Foreign Minister Chrystia Freeland said Tuesday she was "greatly" concerned about the move, saying there were "no scientific reasons for this action".

Relations between Ottawa and Beijing have been thrown into crisis by the December arrest of Meng Wanzhou -- the chief financial officer of telecoms giant Huawei -- at the request of the United States.

Washington wants to put Meng on trial on fraud charges for allegedly violating Iran sanctions and lying about it to US banks, and the case has become a major headache for Ottawa.

China detained former Canadian diplomat Michael Kovrig and businessman Michael Spavor in what observers see as retaliation just days after Canada arrested Meng.

Meng is scheduled to appear in court on Wednesday to set a start date for extradition hearings.