A teenage girl has allegedly been sexually assaulted on Rottnest Island, a tourism destination located 30kilometres off the coast of Western Australia. 

The alleged assault happened in a toilet block on Saturday night amid the arrival of tourists, many of them teenagers, in the first week of the school holidays. 

Daily Mail understands that another teenager is assisting police with their inquiries.  

Officers from the sex crime squad travelled from Perth to the island on Sunday afternoon to investigate what allegedly happened to the 15-year-old. 

The toilet block where the alleged assault happened is close to the Hotel Rottnest on Bedford Avenue, near the island’s ferry jetty.