The private operator of Sydney's ferries will put on 400 extra weekly services by mid 2021 after the state government awarded it a $1.3 billion contract.

Under the nine-year deal, French company Transdev will bear the cost of leasing 10 new ferries to expand services on Parramatta River and a further three Emerald-class vessels for routes on Sydney Harbour.

About 280 weekly services are due to start on Parramatta River in the middle of next year, followed by 120 on the harbour by mid 2021.

A population boom along the banks of the Parramatta River is adding to demand for ferry services. Credit:Nick Moir

A company Transdev now owns outright has run the state government-owned ferries since 2012 after the Coalition government decided to put their operation into private hands. The previous contract to operate Sydney Ferries was worth $871 million.