A giant rubber duck took to the waters of Sydney Harbour this morning in a dawn rehearsal for a Sydney Festival event which organisers say will turn the harbour into a "giant bathtub".

The 15m duck, designed by Dutch artist Florentijn Hofman, will sail into Darling Harbour on Saturday to launch the city's summer festival.

Sydney Festival director Lieven Bertels said the eye-catching event will open the festival to new audiences.

"People will see it from the highway, will see it from the harbour, it's five storeys high, and it's just a very quirky way to say 'the festival is on, please join us in the party'", he told the Australian Broadcasting Corporation.

Hofman's oversized ducks have previously been exhibited in France, the Netherlands, Japan, Brazil and New Zealand.

Although known as 'Rubber Duck', the bright yellow creature is made of PVC material and was constructed in New Zealand by a company specialising in large sails, local media reported.

Sydney Festival officials said the duck took three weeks to make, and takes about half an hour to inflate.

Hofman said his giant duck "brings people together".

"We are living on a planet, we are one family, and the global waters are our bathtub, so it joins people," he said at today's rehearsal.

Hofman said that, at a previous display, a woman's car rolled into a harbour when she got out to take a photo of the duck.

After the launch event on Saturday, the giant duck will remain moored in Darling Harbour for the duration of the Sydney Festival until 23 January.