Australia's first driverless passenger train completed its maiden test journey in Sydney on Monday, travelling 36 km between suburbs in the city's northwest.

Australia's first driverless passenger train during a test on the Windsor Road Bridge in Sydney, New South Wales, Australia, July 18, 2018. (Photo: IC)

The 5.9-billion-US-dollar new metro line has 22 driverless trains, and will open to the public later in the year.

"They said it would never happen ... (but) today we see the train tested for the first time," New South Wales Premier Gladys Berejiklian said.

The new northwest metro line has come in 359 million US dollars under budget.

"The project is almost ready," Transport Minister Andrew Constance said, adding that "we're finishing stations, car parks and testing trains to get the northwest rail line open as quickly as possible."