President Xi Jinping sent a sympathy message to his United States counterpart Joe Biden on Friday, broadcaster CCTV reported, a day after the 79-year-old US leader tested positive for Covid-19.

Biden on Thursday insisted he was "doing great", and said he would continue to work while isolating at the White House with mild symptoms.

"I would like to express my deep sympathies to you and wish you a speedy recovery," Xi wrote in the message, CCTV reported.

It is the first public contact between both leaders since their last virtual summit four months ago.

The pair held a video conference on March 18, when Biden warned Xi against assisting Russia in its military offensive in Ukraine. The leaders have known each other for more than a decade, having travelled together when both were vice-presidents.

Earlier this week, Biden told reporters he expected to speak with Xi sometime in the next 10 days.

Biden sidestepped a question about what he might have to say to Xi about US tariffs on Chinese products. “I’d tell him to have a good day," Biden responded.

Biden also appeared to cast doubt on a trip reportedly planned by US House of Representatives Speaker Nancy Pelosi to Taiwan next month. "I think that the military thinks it's not a good idea right now, but I don't know what the status of it is," he had said.

Beijing has said any such visit by Pelosi would seriously undermine China's sovereignty and territorial integrity. (Additional reporting by AFP)