Australia's New South Wales government is trying to sell a 51 percent stake in Sydney Motorway Corporation (SMC), the company building the A$16.8 billion ($13.2 billion) WestConnex project, which links Sydney's center with its fast-growing western suburbs. Preliminary bids for a 51 percent stake were due on Monday with final bids due by mid-year.

Three people familiar with the bidding process told Reuters local pension funds IFM Investors and AustralianSuper and Canada's La Caisse de dépôt et placement du Québec (CDPQ) were each part of separate consortia bidding for the stake.

The sources did not want to be identified because the details of the sale were confidential.

The country's competition watchdog on Monday evening said it would review the bid made by the AustralianSuper consortium, which also includes Transurban Group.

The regulator would investigate whether the potential part-ownership by Transurban, which has investments in other Sydney toll-roads, would deter competition and enable the listed toll-road operator to increase prices.

A spokesperson for Transurban could not immediately be reached for comment.

AustralianSuper and IFM declined to comment. Representatives of CDPQ did not immediately respond to email and phone requests seeking comment.

Local media have reported two other groups bidding for the stake in the project.

The unfinished 33-kilometre (20.5 miles) road will be built in three stages and is the largest transport project since the Sydney Harbour Bridge, which was completed in 1932.

A spokesman for Stuart Ayres, the state government minister responsible for project, said the binding bid phase would commence "shortly" but that the government would not speculate on potential participants vying for the stake.

(Reporting by Paulina Duran in SYDNEY; Editing by Sam Holmes)

By Paulina Duran