A shark sighting caused two of Melbourne's most popular beaches to be closed for two hours on Sunday, but there was no sign of panic.

Elwood and St Kilda beaches were closed around midday after a 1.5-metre shark was spotted 150 metres off St Kilda marina just after 11am.

Elwood Life Saving Club president David Rylance said it was the first time in 10 years the water at Elwood beach had been evacuated during patrol times due to a shark sighting, and only the third time in his 25 years with the club.

At Elwood, sailboarders continued to sail and at St Kilda, many swimmers splashed in the depths like normal, despite life savers warning beachgoers they should stay out of the water.