Britain's Queen Elizabeth II records her address to the UK and the Commonwealth in relation to the coronavirus outbreak at Windsor Castle, west of London on Sunday. Photo: AFP

A man who entered the grounds of Windsor Castle, where Britain's Queen Elizabeth II is spending Christmas, has been arrested and is being held on suspicion of possession of an offensive weapon, police said on Saturday.

The 19-year-old from Southampton in southern England did not enter any buildings and security processes were triggered within moments, Thames Valley Police said in a statement.

The 95-year-old monarch, who has spent much of the COVID-19 pandemic at Windsor Castle, was celebrating Christmas there with her son, Prince Charles, his wife, Camilla, and other close family.

"The man has been arrested on suspicion of breach or trespass of a protected site and possession of an offensive weapon," said Thames Valley Police Superintendent Rebecca Mears.

She added that members of the royal family had been informed about the incident and that police did not believe there was a wider danger to the public.

The incident took place at about 0830 GMT.

Charles, Camilla and other royal family members were pictured later in the morning arriving for a Christmas church service at St George's Chapel within the Windsor Castle complex.

There was no suggestion that any of the royal family's plans had been disrupted by the incident.

Security breaches at royal residences are rare. The most serious one in the queen's reign happened in 1982, when an intruder climbed a wall to enter Buckingham Palace, her London home, and wandered into a room where she was in bed.

The queen made no public appearance on Saturday. In a pre-recorded Christmas message to the nation, she spoke of the loss of her husband, Prince Philip, who died in April aged 99. 

Reuters