Sydney  - A shark attacked a man who was snorkelling just six metres from the beach at Port Kennedy, south of Perth in Western Australia on Saturday, news reports said.

A search by police and emergency services with boats and a helicopter failed to find the 51-year-old man and at least one eyewitness reported seeing blood in the water, ABC radio reported.

It said a large shark had been spotted in the area and the man's family had requested that it should not be hunted and destroyed.

The man, who lived locally, was snorkelling with his 24-year-old son, who called for help when his father was attacked.

Authorities closed the beach to swimmers as the search for the man continued. (dpa)