The government did not answer specific questions about the target date but said converting the line to metro standards was a “massive undertaking”, and it would update the public on an opening date when it was possible to do so and when it was confident it could deliver on that date.

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“This next stage of testing is just one important step on the way to that,” a spokesperson said.

“The T3 Bankstown line was more than a century old and a notorious bottleneck on the rail system that often resulted in disrupted journeys in that part of Sydney.”

The existing M1 line between Tallawong and Sydenham via the CBD was also closed over the weekend to finish integration and testing of control systems that will enable passenger services to be extended to Bankstown next year.

The installation of 170 mechanical gap fillers to platforms at eight stations along the converted line between Sydenham and Bankstown has added complexity to the operation of driverless trains. The small hydraulic platforms extend to the metro carriages before screen doors open, ensuring that commuters can safely step on and off when the line opens.

Sydney Metro, the agency overseeing the project, has also been embroiled in a dispute with Fire and Rescue NSW over a lack of fire hydrants on platforms at nine stations.

The M1 line comprises the first stage between Tallawong and Chatswood, completed in 2019 at a cost of $7.3 billion, and the city and southwest sections which are costing a total of $21.6 billion.

The final stage between Sydenham and Bankstown had been planned to be opened in late 2025 after a 12-month shutdown of the old line, but was later delayed until some time next year.

Under the original plans of the previous Coalition government, the south-west section was meant to open in 2024 at the same time as the rest of the second stage between Chatswood and Sydenham.