Denmark’s Australian-born Crown Princess Mary and her family are in isolation after her eldest son, Prince Christian, was diagnosed with the coronavirus.

The Danish royal family confirmed the news on Monday (local time) after being notified of an outbreak at the 15-year-old prince’s school.

“The Crown Prince and Crown Princess were informed yesterday, Sunday 6 December 2020, of a local outbreak of COVID-19 at Tranegårdskolen in Hellerup,” it said.

“Prince Christian has subsequently tested positive for COVID-19.”

The Danish royals in Switzerland in January 2020. Photo: AAP

Tasmanian-raised Princess Mary, her husband Prince Frederik and Christian and his siblings, Princesses Isabella and Josephine and Prince Vincent, are in isolation.

It is not known if Prince Christian, who is second in line for the Danish throne behind his father, is showing any symptoms of the virus. He has not had any recent contact with members of the extended royal family.

His diagnosis came with Denmark about to implement further lockdown measures in parts of the country to curb a spike in coronavirus infections.

Restaurants, museums, cinemas and other cultural institutions will have to close on December 9 in 38 of 98 municipalities, including Copenhagen. Students in upper primary school, high schools and universities will be sent home.

“We are entering a new phase of the epidemic, it is a phase where we are seeing exponential increases in the infection curves,” Health Minister Magnus Heunicke said on Monday.

In the past 24 hours, 2026 infections were confirmed from more than 78,000 tests and 328 people had been hospitalised. Mr Heunicke said that number was likely to rise to 400 in the coming week.

The restrictions will remain until January 3.

Countrywide restrictions already in place will be extended until March.

-with AAP