BEACHES have re-opened after a massive pack of more than 100 sharks was seen about 600m off popular Trigg Point earlier today.

The sharks were spotted about 12.25pm today by pilotson board the Surf Lifesaving Westpac Helicopter.

City of Stirling Beach services coordinator John Snook told ABC radio this afternoon the sharks were believed to be juvenile bronze whalers feeding on a school of baitfish.

He said the size of the school of sharks was "absolutely unusual."

Beaches 1km north and south of Trigg Point were closed for several hours with shark alarms going off to get people out of the water. They were reopened around 2pm.