Construction work to extend metro railway tracks from Sydney’s north west into the city has started.

Work is taking place at the end of the Metro North West Line at Chatswood, where Sydney Metro will be extended as part of the City & Southwest project.

The work, known as the Northern Connection, is being done within the existing railway corridor while minimising impacts to train services on the T1 North Shore line.

Excavators recently moved 330 tonnes of soil and piling rigs drilled 34 holes, each up to eight metres deep.

This foundation work will help create the ramp-like structure for metro trains to enter and exit the new twin metro tunnels at Chatswood.

About 7,500 tonnes of material will be excavated and a section of the existing suburban railway line will be re-positioned to create the structure, which is expected to link into the tunnels in 2022.

About 130 workers from Systems Connect – Sydney Metro’s contractor delivering line-wide work on the City & Southwest project – had 48 hours to get the work completed in time for the resumption of Monday morning train services.

When complete, the Northern Connection will create a seamless metro railway journey from Tallawong under the Harbour, through the city and beyond to Bankstown in 2024.