A 50-year-old man suffered a serious head injury after being hit on the head by a falling rock in a park, police say.
The man was out walking with his family near to the duck pond in Williamson Park, Lancaster when the incident happened.
Police say he suffered a serious head injury from the falling rock and was taken by ambulance to the Royal Lancaster Infirmary. His condition is described as critical.
The incident happened at shortly before 6pm yesterday (Saturday, April 22).
Police also say, while at this stage this appears to have been a tragic accident an investigation is underway by Lancashire Police and Lancaster City Council.
Susan Parsonage, Lancaster City Council's chief executive, said: "All our thoughts are with the gentleman and his family and we send our best wishes for a speedy recovery.
"The council is now working with the police to investigate what led to this terrible incident."
Anyone with information is asked to call Police on 101 quoting log number 1164 of April 22.