The boy, 15, told police that a four-metre shark had taken a chunk out of his surfboard as he was being towed by a boat carrying two mates off Wangi Wangi.

He said he was forced to jump from the board and swim to safety as the shark dragged his board underwater.

The story has since been determined as a hoax.

"We obviously have serious concerns about the misuse of emergency services as well as government agencies resources which could have been used in other areas,'' Senior Constable Tony Tamplin said.

Police are deciding whether to formally caution the youth using the Young Offenders Act.