China has stepped up efforts to discredit a US intelligence probe into the origins of coronavirus, as hopes fade there will ever be conclusive evidence about whether COVID-19 escaped from a laboratory or was transmitted naturally to humans through animals.

Days ahead of the release of the Joe Biden-commissioned probe into whether the virus leaked from a laboratory in the central China city of Wuhan, Chinese diplomats and state media are promoting alternative theories suggesting COVID-19 originated in the United States.