Up to 12 rail stations may be built between Sydney's inner city and Parramatta and Westmead under emerging plans for a Metro West train line.

Fairfax Media understands the Metro West line is being planned to use extra tracks and overtaking lines to combine both express trains between Parramatta and the central city, as well as trains stopping at multiple new stations through Sydney's west and inner west.

Under Mike Baird's timetable, the Metro West line was to be built next decade, and be "operational in the second half of the 2020s". Credit:Fiona Morris

The government has committed only to building stations for the line at the Bays Precinct around Rozelle and Olympic Park.

But a total of eight to 12 stations are likely to be included on the line when more detailed plans for Metro West, one of the last major commitments by former premier Mike Baird, emerge later this year.