Hundreds of metres of new elevated rail will be built through Melbourne's outer north when the South Morang line is extended to Mernda.

Three rail bridges, including an 800-metre rail bridge over the planned Mernda town centre, and two rail underpasses, will be built.

The eight-kilometre rail extension is due to open in 2019, with two new stations.

A potential third station at Hawkstowe Parade may be built also, with tenderers to be invited to submit a price for what this will cost. There are two short-listed bidders.