Sussex Police is investigating a 'serious assault' on a rough sleeper at the Royal Pavilion Gardens in Brighton.
The gardens were sealed off by police after the incident which left the man in a 'critical' condition with serious head injuries.
A Sussex Police spokesperson said: "Police are investigating a serious assault on a man at Royal Pavilion Gardens in Brighton.
"The incident is reported to have occurred close to Brighton Museum and Art Gallery about 11.55pm on Tuesday (August 7).
"The victim, who is a rough sleeper believed to be in his 50s, has been taken to Royal Sussex County Hospital in Brighton with serious head injuries. He is currently in a critical condition.
"The gardens are likely to remain closed for a number of hours as forensics investigations are carried out, and members of the public are asked to avoid the area."
A tweet from Brighton Museums said: "Due to a serious incident in the Royal Pavilion Garden, Brighton Museum and The Royal Pavilion will remain closed until further notice."
Sussex Police asked anyone with any information to report it online or call 101, quoting Operation Dickenson.
Alternatively, call Crimestoppers anonymously on 0800 555 111.