Traffic flow along Keira Street will change on Wednesday night as the GPT development reaches a new stage.
At present there are two lanes of traffic open on the eastern side of Keira Street, between Crown and Market streets.
Tomorrow night, after the last buses have left the city, construction crews will swap the jersey barriers around, closing off the eastern side and reopening the western lanes.
GPT West Keira development manager Steven Turner said the changes would allow work to continue on the underground tunnel linking the new building with the existing Crown Central.
"At the moment you've got two lanes of traffic on the road on the eastern side while we excavated the tunnel on the western side," Mr Turner said.
"What's happening on Wednesday night is we've finished the tunnel excavation on the western side and put the road back on top and we're about to swing across over to the eastern side.
"It's a pretty straightforward closure."
The tunnel excavation will also affect pedestrian access along Keira Street.
The footpath along the western side will be reopened while access on the eastern side will be limited.
A section of the eastern footpath will be closed between the mall and the old Regent Cinema during excavation.
People wanting to reach the shops north of the Regent will need to cross to the western side and then cross back at the Market Street intersection.
"Those works have already started, regarding breaking through the Crown Central building. So that stretch of footpath will be out of play," Mr Turner said.
The project is due to be completed in the third quarter of 2014.