A worker on the royal estate in Sandringham in Norfolk is believed to have been underwater "for a number of minutes" after the grasscutter he was riding went into a lake.
The man, in his 30s, had apparently become trapped underwater by the grasscutter. He was taken to Addenbrooke’s Hospital by air ambulance where he remains in a critical condition.
Emergency services were called to the scene at Lower Lake, close to the B1440 at around 1.30pm on Monday.
Two police officers and a colleague from the estate retrieved the man from the water and began CPR before paramedics arrived.
Norfolk Police and the Health and Safety Executive are continuing to investigate the accident.
More top news
Dry and cold through much of the night with a frost for some by morning. It will turn cloudier during Saturday with a few spots of rain.
Police are warning teenagers are putting their lives at risk by carrying out dangerous stunts on the streets of Northampton.
A dog has died after it was attacked by four other dogs in a Norfolk village.