Ractopamine is used by pork producers in some countries to make leaner pigs but China does not allow its use and does not tolerate residues of the compound in imported meat.

China will also strengthen inspections for the residue in all pork imports from Canada, Xinhua reported, citing customs.

Canadian government officials said this month they had been warned by China that it would step up inspections of meat imports after "recent cases of non-compliance" in pork shipments.

The Xinhua report said customs authorities in the port of Nanjing had detected ractopamine residue in a batch of pork on 3 June.

China said it would open all containers of Canadian meat and meat products and, in some cases, 100 percent of the contents would be inspected.

China has already halted pork imports from two other Canadian producers, Olymel LP and Drummond Export, because of labelling problems.

It has also blocked imports of Canadian canola seed.

Trade problems between the two countries comes as China has been demanding that Canada returns a Chinese tech executive who is facing extradition to the United States.