A much-hyped underground rail service will open with a soft-launch timetable before moving to turn-up-and-go trains.

Melbourne's $15 billion Metro Tunnel will open to the public in early December, with 240 extra services to run alongside the existing timetable for the Sunbury, Cranbourne and Pakenham lines.

Extra services in the "summer start" period will run every 20 minutes from 10am to 3pm between Westall and West Footscray on weekdays.

Weekend services will run every 20 minutes from 10am to 7pm between Westall and West Footscray, every 40 minutes from East Pakenham and 60 minutes from Sunbury.

Regular Sunbury, Cranbourne and Pakenham services will continue to run through the City Loop until the full turn-up-and-go timetable takes effect on Sunday, February 1.

Those lines will ripp

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