It was duck mania in Darling Harbour as 60,000 people turned out to watch Dutch artist Florentijn Hofman's Rubber Duck sail in. The sound of quacking rose above the hubbub of the crowd, and bath-time rubber ducks rained down over the scorching Cockle Bay.

It may not have been the opening event but the arrival of the oversized yellow bird signalled the 36th annual Sydney Festival was truly under way.

The honour of opening the festival went to performance artist Humphrey, who ran a 42-kilometre marathon on a treadmill while an hourly flash mob kept the audience entertained with dance. The flash mob of volunteer Sydney residents had been rehearsing for three months.

Judith Stephens, 60, says she got involved because such events bring Sydney together. ''Sydney is a city with a soul, Sydney Festival exposes that.'' The self-proclaimed adventurer believed this was a great incentive to get all ages ''out of the house and moving''.

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Over the next 21 days, festival organisers will rely on 250 volunteers to facilitate many events. Margot Thomas, 32, is studying events management and is a first-time volunteer. ''This is a great way for me to … get some real experience,'' she said.

The festival runs to January 27.