A PTA spokesman said the authority was working to resolve the issue and that the Transperth and Transwa websites had been partially restored on Thursday evening.

In the meantime, customers of the SmartRider electronic ticketing system will not be able to check their balances online.

Passengers can call the Transperth InfoLine on 13 62 13 for route and timetable information.

Several of the sites were still affected on Friday morning.

- AAP