Beaches near Perth, in Western Australia, were closed for a while on Tuesday (March 19) after an unusual large school of sharks was spotted just offshore.

Local media said the group numbered around 100 sharks, about 600m off a popular beach.

The crew of a surf life saving helicopter spotted the animals, which were thought to be juvenile bronze whalers feeding on a school of baitfish.

A local beach manager told ABC radio the size of the school was "absolutely unusual."

Beaches 1km north and south of the scene of the sighting were closed for several hours with shark alarms warning people to get out of the water, local media reported