Recreation and all other activities at Leighton Beach and Port Beach continue after being closed for over an hour due to sightings of two whale sharks.

The sharks were originally spotted 500m from shore and were tracking south towards Fremantle.

Fremantle City rangers attended the beach earlier and advised swimmers of the closure.

Surf Life Saving WA's Craig Bowley told WA Today it was unusual for whale sharks to journey so far south, though they had been identified in Perth waters several times last year.

Whale sharks are mainly sighted at Ningaloo Reef during April.

Bowley said SLSWA had completed an aerial inspection and there were no other signs of a six-metre whale shark or another smaller shark.

Whale sharks are harmless to humans because they feed on other marine life. They can grow up to 20 metres in length.

Bowley said it seemed the six-metre whale shark had attracted the attention of the other three-metre shark, prompting the quick closure of the two beaches.