Heir to the throne Charles, 71, is displaying "mild symptoms" of the COVID-19 illness but is in good health and spirits as he self isolates at Birkhall in Scotland, a spokesman said on Wednesday.

Camilla, 72, who is also at Birkhall, in Aberdeenshire, has tested negative for the virus, so is separating herself from the prince.

Doctors believe future king Charles became contagious on March 13 - the day after he last saw his mother, the Queen.

Buckingham Palace said the 93-year-old monarch, who is staying at Windsor Castle with the 98-year-old Duke of Edinburgh, remains in good health and is following all appropriate advice.

Philip was not with the Queen at Buckingham Palace when she last met Charles on March 12.

Charles has spoken to both his sons the Duke of Cambridge, who is in Norfolk with the Duchess of Cambridge and their young children, and the Duke of Sussex, who is in Canada.

He has also been in touch with the Queen.

The prince's last public engagement was on March 12 when he attended a dinner in aid of the Australian Bushfire Appeal in London.

He later had a number of private meetings with Highgrove and Duchy individuals, all of whom have been made aware of the situation.

On March 10, he was with Monaco's head of state Prince Albert II, who has since tested positive for coronavirus.

Charles is not believed to have shaken hands with Prince Albert but attended a roundtable meeting with him at the WaterAid Summit in London on that day.

The prince was pictured practising namastes instead of handshakes at his public events, including when the royals gathered for the Commonwealth Day service at Westminster Abbey on March 9, and a Prince's Trust event on March 11.

"The Prince of Wales has tested positive for coronavirus. He has been displaying mild symptoms but otherwise remains in good health and has been working from home throughout the last few days as usual," Clarence House said.

"In accordance with government and medical advice, the prince and the duchess are now self-isolating at home in Scotland.

"It is not possible to ascertain from whom the prince caught the virus owing to the high number of engagements he carried out in his public role during recent weeks."

A source said his doctor's most conservative estimate was the prince was contagious on March 13.

A small number of people living and working at Birkhall remain at the residence and are self-isolating.

The source said the prince was up and about and not bedridden.

Medical advice is that it is unlikely to escalate into a more serious case.

A Buckingham Palace spokeswoman said: "Her Majesty the Queen remains in good health.

"The Queen last saw the Prince of Wales briefly after the investiture on the morning of March 12 and is following all the appropriate advice with regard to her welfare."

Australian Associated Press