The New South Wales Government is spending at least $6 million on its "Tomorrow's Sydney" advertisements, a campaign to promote its infrastructure and transport vision for the city.

So far the campaign has primarily consisted of posters on buses and trains, but Transport Minister Andrew Constance said new TV ads would begin on Sunday.

They will warn Sydneysiders that construction for the $2 billion light rail project will be a lengthy and difficult process.

"Our message to the city is: everyone is going to be disrupted by this, everyone must be patient and work together," Mr Constance said.

"We want to keep the city thriving during what will be one of the most difficult infrastructure builds this state has ever embarked on."

Mr Constance said the campaign had already cost taxpayers $6 million and he was prepared to spend more.

"Let's really put this into perspective; we are transforming Sydney," he said.

"This is not a government that promises things and doesn't get on with it.

"We are building — we need people to understand how this is going to affect their lives and we're having to invest to do so."

Bid to minimise disruption to Christmas retail

The minister also announced a change in the construction timetable for the light rail, aimed at minimising impact on CBD shopping this Christmas.

Work on George Street related to the relocation of utilities was set to begin on October 23, but will now start on October 5 — a day after buses are taken off George Street.

"These critical investigative works are the most complex in terms of utilities — gas, electricity," Mr Constance said.

"We need to get in and do significant assessments on how utilities will be impacted as a result of us laying a new rail track through the heart of the city."

Roads Minister Duncan Gay said the decision to change the construction timetable would lead to a better outcome for businesses and shoppers at Christmas.

"The bad news is we're starting early," Mr Gay said.

"The good news is we're minimising disruption during that key Christmas period."

'Be patient', minister tells public

Mr Constance said Sydneysiders would be able to go online and work out the best way to navigate the city during the construction.

"There are some 70 projects happening across Sydney at this point in time. It's not just the light rail," he said.

"So our message is be patient, think of the bigger picture, because once this happens this is going to be a completely different city."

Mr Constance said by Christmas 2016, a new pedestrian boulevard for George Street should be finished.

The light rail is scheduled for completion in 2018.

Opposition transport spokesman Ryan Park criticised the Government for changing the construction timetable.

"This must be the only government in the entire world that's forgotten that Christmas occurs on the same day each and every year," he said.

"Why did they wait until August to announce the changes to Christmas to help retailers when retailers, pedestrians, city users and the Opposition have been screaming for months about the problems that lie ahead?

"In eight weeks' time, this city will grind to a halt — George Street will essentially be shut down. Eight weeks out and they make more changes?"