This followed after Queen Elizabeth II traveled home to Buckingham Palace after her usual weekend break at Windsor Castle in Berkshire.
The Queen returned on Mar. 16 in the afternoon. The Royal Standard flew above the head of the state's official London residence.
London is on an alarming state as it has 407 of the 1,543 confirmed coronavirus cases and six of the 36 deaths in the U.K.
A police van was parked outside the royal residence with one man wearing a white hazmat suit and mask while several officers are also in attendance donning face masks and protective gloves.
An onlooker said, "Some of the officers had masks on and the ambulance workers had full white suits on. It was pretty scary to see."
His first fear was that it was a case of coronavirus because of their protective clothing.
It happened just after midday in the afternoon on Mar. 16.
According to the London Ambulance Service spokesman, they were called at 12:07 PM on Mar. 16 to a reported incident on Buckingham Gate, Westminster.
They sent an incident response officer, a medic, and an ambulance crew in a car to the scene. They treated one person and took him to the hospital.
It is too early to verify if this is coronavirus-related, a source said.
According to a Scotland Yard spokesman, designated officers came across a sick man on the Spur Road at the junction with Birdcage Walk in Westminster at 12:05 PM on Monday, March 16.
Officers called the London Ambulance Service to provide treatment for the patient.
The man was sectioned under 136 of the Mental Health Act and sent to the hospital.
How the royals are dealing with coronavirus
The Queen left the palace a week early to retreat to Windsor, in the midst of the growing novel coronavirus pandemic.
The Queen also had to cancel her several large scale events after Boris Johnson's latest updates over the coronavirus outbreak.
According to a palace spokesman, "In consultation with the Medical Household and Government, a number of public events with large numbers of people due to have been attended by The Queen, and other Members of the Royal Family, in the coming months will be canceled or postponed."
Prince William and Kate Middleton, Duke and Duchess of Cambridge, recently swapped an annual St. Patrick's Day parade for a video message of support dedicated to the Irish Guards on Tuesday.
The cancellation of the parade was symbolic, arriving as the palace is in the process of reassessing their royal duties in the advent of COVID-19.
The royal pair plan to shift the focus of their work to providing support for the nation. Their attention on primary causes will be temporarily diverted from young children (Kate's primary work) and conservation (William's key cause).
"The Cambridges are not in the vulnerable sector and they want to help. Their aides are going through the latest government advice but it's fair to say the focus of their work will shift. Supporting the community and vulnerable people in society is more important right now," a source said.