The cost of building the light rail line from the city to the eastern suburbs is likely to blow out to around $2.2 billion – $600 million more than first budgeted.

Transport Minister Gladys Berejiklian will not confirm the final figure, but sources said the size of the blow-out has caused consternation within the government, with major work on the project not due to start for half a year.

NSW Transport Minister Gladys Berejiklian will not confirm how far over budget the light rail line from the city to eastern suburbs will be. Credit:Nick Moir

"People are agog that they have managed to get away with it," one source said.

The cost of the light rail line, which is planned to run from Circular Quay to George Street through Surry Hills to Randwick and Kingsford, is also dismaying public transport advocates concerned the price tag will prevent future governments from building new tram lines.