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 bright to start, turning cloudier with rain later
Heavy showers quickly clearing leaving a sunny morning
Heavy showers overnight. Fine for most of Sunday.