WATER police have pulled a body from Sydney Harbour this afternoon after a woman went overboard while riding the Manly Ferry.

Emergency services were called about 2.20pm after reports a female passenger had gone in the water near Bradleys Head.

The Westpac Life Saver Rescue Helicopter was called in to help with the search, which ended shortly after when police found her body.

Marine Area Command officers were assisted by North Shore Police.

Paramedics treated the woman but she could not be revived.

A Westpac spokesman said it was unclear how the woman died but witness reports indicated she took her own life.

The spokesman said the height that she entered the water from would have meant that she went quite deep.

He said people could also suffer cold-water shock when they entered low temperatures quickly, causing them to take a breath under water and down. But he said investigations into the exact cause could have to be carried out.

A report will be prepared for the coroner.

If you or someone you love is in crisis or needs support right now, please call Lifeline on 13 11 14 or BeyondBlue on 1300 224 636. If it is an emergency please call 000.