A teenage girl who claimed she was sexually assaulted and slashed with a knife at a bayside beach in Melbourne this week fabricated the story, police say.

The 18-year-old told detectives that she was walking along Edithvale Beach about 5.30pm on Tuesday when she was attacked at dusk by a man who held her at knife-point and sexually assaulted her.

Man hunt ... Police tape and a tarpaulin cover the 'crime scene' outside the public toilet block at Edithvale beach, where the young woman claimed she was raped and stabbed. Credit:Penny Stephens

However Victoria Police said in a statement today that detectives now were treating it as a false report, and reassured the community that there were no safety concerns.

"Information was provided to detectives this morning which has revealed that no offence occurred," the statement said.