A mechanical worm nicknamed Nancy has munched its way from Marrickville to Waterloo to complete the first 3.1-kilometre tunnel of Sydney's Metro City project.

The mega machine was greeted by Premier Gladys Berejiklian when it burst through rock at Waterloo on Friday after tunnelling for almost six months.

Ms Berejiklian says the metro project, featuring driverless trains, will “change lives”.

“The people of NSW wanted us to keep building and that’s what we are doing,” she told reporters on Friday.

The mega boring machine will continue tunnelling towards Barangaroo via new stations at Central, Pitt Street and Martin Place as part of the coalition’s Metro City project.

The city line is due to be completed in 2024 and will link Sydenham to Chatswood.

The government’s first metro route from Rouse Hill to Chatswood is almost complete and due to open in May.