Public transport users will be able to top up their Opal cards at machines at selected train stations, ferry wharves and light rail stops from next year.

The design of the machines – some of which will also allow travellers to purchase disposable tickets – is part of a $100 million package of additions to the public transport smartcard.

From next year, public transport users will be able to top up their Opal cards at some train stations, ferry wharves and light rail stops. Credit:James Alcock

Transport Minister Gladys Berejiklian will announce on Wednesday that the testing of top-up machines will start this week, and about 350 machines will be installed across the state's transport network over the next 12 months. The machines will not be at all stations, wharves or light rail stops.

But Ms Berejiklian said they should provide "coverage for around 99 per cent of customers".