China on Thursday said it had never asked US diplomats to undergo Covid-19 anal swabs, following American media reports that State Department personnel had complained of being subjected to the intrusive test.

China -- which has largely brought the virus under control domestically -- said last month that anal swabs can be more effective than normal throat and nose swabs as the virus can linger longer in the digestive system.

But Beijing rebuffed reports from Vice and Washington Post -- citing US officials -- that State Department employees in China had been given the test "in error," despite diplomats being exempt from the procedure.

"China has never requested US diplomatic personnel in China to undergo anal swabs," foreign ministry spokesman Zhao Lijian said at a regular press briefing Thursday.

Officials in China have used anal swabs to test people it considers at high-risk of contracting Covid-19, including residents of neighbourhoods with confirmed cases as well as some international travellers.

State media reports that anal swabs had been used in Beijing during a small outbreak in January caused a social media uproar, with many commenters on Twitter-like Weibo reacting with a mix of horror and amusement.

But officials acknowledged it would be hard to use anal swabs as widely as the other methods, which have been used to test millions in mass campaigns, as the former technique was "not convenient."