A man armed with a knife is believed to have suffered serious facial injuries when he attacked a man in a caravan in Brighton.
Sussex Police said the attacker covered in blood after the incident in Preston Park in the early hours of Thursday.
The attacker and his victim, who was staying in the caravan at the park, were involved in a struggle but the victim was not injured.
Police said the victim was lucky not to have been seriously injured.
It is not thought the two men knew each other.
A spokeswoman said they wanted to track down the attacker urgently and described him as white, aged between 40 and 50, with receding black hair which was going grey.