A man believed to be one of the Queen's employees was left fighting for his life on Monday night after he fell into a lake.
The man, who is said to be in his 30s, was riding a sit-on lawnmower at the time in the grounds of the Sandringham Estate.
Police officers rescued the man from the lake and attempted to resuscitate him until paramedics arrived. He is said to be in a critical condition with life-threatening injuries.
It has been reported that the Queen, who was at Sandringham at the time of the incident, is being kept aware of the details.
Her Majesty was hosting a private meeting with members of the Welsh Corgi League and their dogs in her garden at the time.
The Queen, a well known Corgi lover and patron of the league, chatted with members and petted their dogs for around half an hour.
The man was flown by air ambulance to Addenbrooke's Hospital in nearby Cambridge.
The lake in question is Lower Lake, between the estate offices and Sandringham House.
The 600-acre Sandringham Estate lies in the heart of the Norfolk countryside. It is the country residence of the Queen and Prince Philip and is where the royal family traditionally celebrate Christmas.
It was reported earlier this year that the monarch gifted Prince William and Kate Middleton a house in the grounds. Amner Hall lies two miles east of the main house and is said to be undergoing major renovations as they begin family life with the arrival of the royal baby.