SYDNEY - Tens of thousands of fans waving pink flags are expected to line Sydney Harbour's foreshore on Saturday to welcome back round-the-world sailor Jessica Watson.

The 16-year-old's homecoming is expected to rank among the biggest events in Sydney as the NSW Roads and Traffic Authority prepares for a huge crowd. It has classified Watson's arrival as a Class One event - the same rating it gives to New Year's Eve and the Mardi Gras.

NSW Maritime is expecting up to 3000 boats on the harbour, about the same number that farewell the Sydney to Hobart race fleet each Boxing Day.

When Australian Kay Cottee, the first woman to complete a solo nonstop circumnavigation of the globe, returned to Sydney Harbour in 1988 she was met by a crowd of 100,000 people.

Watson is expected to complete her solo, nonstop voyage on Saturday, sailing through the official finish line at Sydney Heads about 1.30pm NZT.

One hour later, after her passport has been checked by Customs on board her yacht, Ella's Pink Lady, she will step on to land for the first time in close to seven months into the arms of her parents at the Opera House.

- AAP