NSW Transport Minister Andrew Constance is concerned that too few commuters have prepared for the biggest change to Sydney's bus network in decades, warning of significant traffic disruption on Tuesday when the city returns to work after the long weekend.

While Sunday was the first day of new bus timetables and routes, the biggest test of the sweeping changes is Tuesday when more than 630,000 bus commuters return to the city.

Speaking on the eve of the biggest challenge of his time in the transport portfolio, Mr Constance said it would take at least a month to bed down the changes because such a large number of commuters needed to adjust their behaviour.

"It's not going to happen overnight, and there are serious challenges as a result of people having to change," he said on Monday.

"We are going to see traffic problems – we are not hiding from that."

New network

The bus network has been changed to allow construction work to begin on a $2.1 billion light rail project, which will connect Circular Quay to Randwick and Kingsford via George Street and Central.

It means almost all bus commuters travelling into the CBD in the morning will be affected by the closure of parts of George Street to traffic for the construction of the light rail line.

Mr Constance said one of his major concerns was that not enough commuters had planned their journeys into the city. He again urged them to read the My Sydney website for details of the changes, and to get to work earlier or outside peak travel periods.

"It is going to take a little bit of time to get used to the change, and there will be some major teething issues until the city finds its rhythm again," he said.

The changes would result in buses on Elizabeth Street increasing from 179 to 201, which would create "a difficult sticky point".

Transport authorities were also doing their "level best" to work with delivery vehicle drivers, and Mr Constance also urged people not to drive into the CBD unless it was necessary.

Permanent havoc

With the government readying for a difficult few weeks, Opposition leader Luke Foley said the "short-term pain won't deliver the long-term gain" for the city, and the light-rail project would wreak "permanent havoc on east-west trips". He cited Infrastructure NSW concluding in 2012 that light rail running along George Street would not work.

"Over weeks and months ahead, as the CBD light rail construction ramps up, congestion will gridlock the city," he said on Monday. "This will mean a permanent congestion nightmare for the city forever more with 66-metre tram sets blocking all motor vehicles travelling east-west through the city."

He also criticised the government for a lack of compensation for affected businesses.

Mr Foley, who favours alternative arrangements for buses instead of a light-rail line through the CBD, said he was most concerned about the impact on Elizabeth Street from a large increase in buses, which could result in long lines of vehicles.

However, Mr Constance accused Mr Foley of "sniping from the sidelines" and said it was in Labor's DNA to tear up contracts and not support public transport.

"We have got an extra 150,000 coming into the city over the next 10 years – we can't just keep putting more buses on Sydney streets," he said. "We are biting the bullet here and we are going to transform the city and that means that streets like Elizabeth Street will be a pain point."

Choke points 

The Rail, Tram and Bus Union warned that potential choke points would be Wynyard, Circular Quay, and Gresham Street.

The union's bus division secretary, Chris Preston, said Elizabeth and Park streets were already "choked with cars".

"It is the biggest change to the city's CBD transport in years, so I don't expect it to go smoothly," he said.

"The whole CBD will be a mess. The bus drivers and passengers have to get used to the changes. I expect a conga line of buses across the Harbour Bridge."

Mr Preston said some passengers had noticed old timetables and route maps at bus stops, and some could be left waiting at stops that no longer existed if they had not read about the changes.

"If I was a passenger I would give myself plenty of time to get to work [on Tuesday]," he said. "I'm really just asking passengers not to take their frustrations out on drivers."

Feeling fine

However, Julian Buckell, 55, who is one of about 120 pink shirt-clad helpers who will be assisting commuters as part of the state government's "street team", said he had no concerns.

For three weeks he has distributed some of the more than 300,000 pamphlets and bus route brochures that have been provided to commuters in lead-up to Tuesday.

"It's been fine," Mr Bucknell said. "People are very good about it. It's really not difficult in 99 per cent of cases."

Mr Bucknell, who on Monday was positioned at a bus stop near Town Hall, said the most common question he was asked was simple one: "Where do I get my bus from now?".

Greens transport spokeswoman Mehreen Faruqi said the bus timetable and route changes would exacerbate and reveal fundamental problems in the fare system and accessibility.

Many commuters from the northern suburbs, inner west and eastern suburbs would discover that they needed to change modes of transport, copping two full fares.

"Integrating transport fares, so that people are not penalised for taking multiple modes of transport, is a long overdue change to our fare system," she said.

Construction of the 12-kilometre light rail line is due to be completed by mid 2018, and is intended to help ease congestion in Sydney's CBD by removing 220 buses during the morning peak travel period.