Sydney train commuters have been warned to expect some further disruptions as Central Station undergoes $955 million “open heart surgery” to make way for the new Metro.

Construction will begin immediately after the NSW government on Wednesday awarded the contract to British construction firm Laing O’Rourke.

The upgrade, including new underground platforms and an underground concourse, is expected to be finished by 2022.

It will allow travellers to move easily between light rail, suburban and inter-city trains and the new underground Metro system.

“This is going to untangle Central,” Transport Minister Andrew Constance told reporters.

“We will, in essence, undertake open heart surgery on Central and we’re going to be able to do so without disrupting passenger services on a daily basis.”

Sydney Trains chief executive Howard Collins and Premier Gladys Berejiklian both acknowledged there would be disruptions.

“It is going to be a challenging project but I think it’s going to be a project that at the end of the day will benefit 300,000 [to] 400,000 people a day,” Mr Collins said.

“There will be some disruption – it’s about getting information to people [and] making sure in advance they know [of changes] but the prize is worth waiting for.”

One platform has already closed to allow work to begin, and other platforms are expected to follow.

Ms Berejiklian said she regretted there will be some temporary disruptions but argued “that’s no excuse for not doing it”.

Premier Gladys Berejiklian and Sydney Trains chief executive Howard Collins acknowledged there would be some disruption. Photo: NSW Government

“It would be negligent for us to sit on our hands and not improve Central railway station because it’s going to cause some interim disruption,” she told reporters.

More than 270,000 people use the station daily, with that number expected to rise to 450,000 in the next two decades.

The upgrade also includes the Central Walk, a 19-metre wide underground concourse from Chalmers Street.

Escalators will also open up to platforms 12 to 23.

A bridge over rail lines, connecting Regent Street with Sydney Yard, has already been completed. It will be used for trucks to gain access to the construction site.

Construction will begin immediately. Photo: NSW government

Following the station upgrade, work will continue along the Sydney Metro City & Southwest Project to lay tracks and fit out stations before Metro services start in 2024.

Laing O’Rourke managing director Cathal O’Rourke said the company has developed techniques that will ensure minimal disruption during the four-year build.

“The station needs to be kept running, and its history and heritage protected, as we also upgrade it to the modern transport solution Metro offers,” he said.

The firm also recently completed the $100 million upgrade of Wynyard Station.

It comes after a joint report into meltdowns on the Sydney Trains network said it was vulnerable to disruptions due to its “tangled” system.

The report also blamed a shortage of train crew and rostering issues, which the Rail Tram and Bus Union (RTBU) attributed to the new and more intensive timetable.

A dispute over the enterprise agreement negotiations soured earlier this year and almost culminated in a 24-hour strike across the state.

-with AAP and AAP