India's financial capital has unveiled its first monorail system, a much-delayed project that aims to boost the city's creaking transport infrastructure and ease traffic on its notoriously congested roads.

The first phase of the transit system, which opens to the public on Sunday, will ferry passengers in green, pink and blue carriages along an 8.8 kilometre stretch in the city's east.

The line expected to extend to about 20 kilometres in length and into south Mumbai next year.

Mumbai is known for its poor roads, heaving traffic and a claustrophobic local train network, which carries millions to work each day.

The monorail aims to ease congestion for commuters in the busy eastern suburbs and help connect them with the city's trains.

The city is the most populated in India, with over 12 million people.

When completed, it will have capacity for 100,000 to 200,000 passengers a day, according to the Mumbai Metropolitan Region Development Authority.

But analysts are skeptical of the impact it will have in the densely populated city.

"The fundamental issue is that the project is only half finished. So you can call the current stage just a pilot or a test of the hardware. It will not be a game changer," Ashok Datar, a transport expert, said.

Road traffic issues cannot be solved by railway-based solutions, Mr Datar added.

Others have criticised the costs and delays of the project, built by Malaysia's Scomi Engineering Bhd and its Indian partner Larsen and Toubro, which overshot its deadline by two years and costed $US479 million.

The metro was opened by Maharashtra chief minister Prithviraj Chavan, who is also a member of India's ruling Congress party.

The Congress party is trying to boost its standing and highlight its achievements ahead of general elections due by May this year.

Just last month, prime minister Manmohan Singh opened a swanky new air terminal in Mumbai, complete with a peacock-inspired design and huge art display, part of a lavish $2 billion airport revamp that also ran over budget and schedule.

The project faced various challenges including tight constraints on the site owing to tens of thousands of tightly-packed slum dwellings encroaching on the airport land.

A delayed metro system is also in the works to help decongest Mumbai's suburban roads.

AFP