Bus passengers catching services in the CBD are being delayed by up to 30 minutes, the Transport Management Centre says.

Passengers can use their tickets on Sydney Trains, on the T1 North Shore Line between Chatswood and the city and on the City Circle as an alternative, the centre says.

George Street has been partially closed for roadworks related to the light rail project, setting the scene for traffic upheaval in the city this week.

The George Street closures are southbound between Alfred and King streets and northbound at Hay and Campbell streets.

The roadworks, which began last Friday, are scheduled to last until next Monday, Transport for NSW says.

About 80 bus routes are affected with diversions and temporary stops in place.

Buses that normally use George Street are diverting via King and Elizabeth streets or via Castlereagh Street and buses are using temporary bus stops, the Transport Management Centre says.

All Victoria Road services that normally run to Wynyard will terminate at QVB, George Street, Transport for NSW says.

The light rail line will extend from Circular Quay along George Street to Central Station, through Surry Hills to Moore Park, then to Sydney's eastern suburbs.

The $2.1 billion contract for the light rail project was signed last month and the line is due to open in early 2019.

The contract includes provisions for major works to finish in 2018, meaning major disruptions in the city and suburbs will take just over three years.

Transport Minister Gladys Berejiklian said last month: "This project will provide a significant improvement in public transport in Sydney, as well as creating more than 10,000 jobs for our economy."

- with Jacob Saulwick