Commuters using one of Sydney's busiest train stations in the city's central business district have been told to brace for four years of disruption as the area is redeveloped.

The $1 billion redevelopment of Wynyard Place will include a grand transit hall and a public concourse at Wynyard train station.

It is expected that after the redevelopment the station will be used by 100,000 commuters per day.

A new commercial and retail precinct will also be built, including a 27-storey office tower.

The upgrade will be underway at the same time as large sections of George Street are restricted to pedestrians, while the CBD light rail is built.

After the redevelopment the station will be used by 100,000 commuters per day. ( Supplied: Transport NSW )

Transport Minister Andrew Constance said the construction period would be inconvenient for commuters, but said they would still be able to access the station during construction.

"George Street is transforming into one of the great boulevards of the world," Mr Constance said.

"Commuters will be able to continue to access the station during development, but obviously during construction it is going to be a challenge and we'd ask people to bear with us while we do that."

The State Government said contracts were awarded without going to tender because developer Brookfields put forward an unsolicited proposal for the project.

Part of the development will be the restoration of the historic Shell House on Carrington Street as well as Margaret Street and Wynyard Lane.