Big romantic gestures were the order of the day in Sydney this morning, as Australians got into the spirit of Valentine's Day.

One couple said their marriage vows on top of the iconic Sydney Harbour Bridge, while another groom-to-be proposed on the side of a huge passenger liner.

He has been working on the secret plan for two months with his friend who works on the ship.

The Registry of Births, Deaths, and Marriages estimates that more than 200 people will marry in the state on Valentine's Day.