Chinese President Xi Jinping sent a sympathy message to his United States counterpart Joe Biden on Friday, state 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.

It is the first public contact between both leaders since their last virtual summit four months ago, as ties between the two global superpowers continue to deteriorate over issues including Taiwan, Ukraine and technology sector competition.

The pair held a video conference on March 18, when Biden warned Xi against assisting Russia in its invasion of Ukraine.

The leaders have known each other for more than a decade, having travelled together when both were vice-presidents.

Earlier this week, Biden said that a call with Xi would take place within the "next ten days", weeks after both countries' top diplomats met in an attempt to defuse escalating rhetoric over Taiwan.

Beijing recently blasted a planned trip by US House Speaker Nancy Pelosi to Taiwan. Were Pelosi to go, it would be the most senior-level US official visit to the self-ruled island -- which China claims is part of its territory -- under the Biden administration.