A shark has been sighted at a Sydney beach moments after federal Opposition Leader Tony Abbott got out of the water.

Mr Abbott had just ended a press conference at Manly Beach today when the shark alarm was sounded and swimmers were ordered out of the water.

Tony Abbott ... got out the water just before a shark alarm went off. Credit:Peter Braig

He had spent several minutes in the surf training with a group of young surf lifesavers.

A surfer saw the shark off the beach at the end of the Corso just before 10am.