Prince Charles, the eldest son and heir to Queen Elizabeth II, is isolating after testing positive for coronavirus for the second time, his office said on Thursday.

"The Prince of Wales has tested positive for Covid-19 and is now self-isolating," said a message on the prince's official Twitter page.

"HRH (His Royal Highness) is deeply disappointed not to be able to attend today's events in Winchester and will look to reschedule his visit as soon as possible," it added.

He was due to unveil a statue in the southern city later Thursday. 

The 73-year-old prince also tested positive in March 2020 and spent around a week isolating at the Queen's Balmoral estate in Scotland.

His office did not say when he was last in contact with his 95-year-old mother, who herself has had recent health problems that forced her to take a step back from official duties.

However, she is once again filling up her diary as a year of celebrations began this week to mark her 70 years on the throne.

Charles met several people at a reception in the British Museum on Wednesday, including finance minister Rishi Sunak.