Two girls were sexually assaulted on Brighton beach within half an hour of each other.
Sussex Police said that although the incidents were separate, they were being treated as linked.
Detectives are trying to trace a group of five men who were reported to have been hassling a 16-year-old Swedish student at about 2.30pm on Sunday (7 July).
She was in the sea opposite the Hilton Brighton Metropole hotel with two friends at the time.
As the girls tried to move away, one of the men grabbed the girl and touched her. She managed to get away and reported the attack to police.
The men were described as having an Asian appearance.
At about 3pm an Asian man approached an 11-year-old girl who was in the water with a friend near the West Pier.
The man picked up the victim and threw her in the air before grabbing her and touching her.
She swam and away and reported it to a witness who reported it to the lifeguards on the beach.
Sussex Police said that officers carried out a search of the beach but the man could not be found.
The suspect was described as an Asian man, with dark brown eyes and short black hair. He was wearing white pants.
Detective Sergeant Emily Hoare said: “These two incidents happened near to each other and about half an hour apart. The two victims suffered a frightening ordeal and there must be witnesses as the beach and sea were packed with people as it was a hot sunny afternoon.”
Anyone who has information should contact Sussex police on 101.