The cost of transforming Sydney's Central Station into a gateway that includes a five-star hotel, high-rise towers and a new route for the inner west light rail line is estimated in leaked documents at just over $3 billion.

The internal Transport for NSW documents show the state government will rely heavily on revenue from a large increase in space for shops and offices in and around the station precinct to help fund the revamp.

But they reveal that the scale of the capital works program for Australia's busiest train station means the revenues generated are unlikely to "ever cover all" of the cost.

The total capital costs for the renewal project includes an estimated $750 million to incorporate Sydney's new metro train line into the station. The government has publicly disclosed the total cost of the second stage of building the entire metro train line at up to $12.5 billion – which it has funding for – but has not broken it down.