Dubai's Roads and Transport Authority has issued procurement notices to contractors to look at significantly extending the city's metro network.

The work would involve more than 20 kilometres of tracks being built and a dozen new stations created, if the project goes ahead.

The Green Line extension would be the most significant of the two lines, with 20.6km of new track and 11 new stations, according to a notice published online.

The plan appears to match a scheme outlined almost a decade ago, which was designed to unlock parts of the city with few transport links.

That was to extend the Green Line from its current terminus at Al Jadaf across the Creek to Emaar's Dubai Harbour development and then onto Academic City.

The Red Line would be extended by 3.5km from the current terminus at Rashidiya to finish at Mirdif City Centre, a large suburban mall close to Dubai International Airport, with a single new station built.

The original plan for at least four metro lines was scaled back more than a decade ago.

But a six-station 15km extension to Expo 2020, at an estimated cost of $2.9 billion, was regarded as a major factor in the success of the world's fair, transporting hundreds of thousands of visitors there.

The existing Green Line stations are in Bur Dubai and Deira in the city's old town, while the Red Line cuts through the metropolis in a straight line, connecting the old city and airport to Downtown, Dubai Marina, and Expo 2020 in the far south-west.

The RTA did not comment on the new contracts but in May said it was looking at how to “develop the infrastructure of road networks and means of transportation, including the expansion of Dubai Metro lines”.

Dubai's population of 3.5 million is forecast to reach 5.8 million by 2040, according to a government report last year, with new public transport links crucial to handling that capacity.