NSW Premier Gladys Berejiklian has brushed off concerns a new private bus operator in Sydney's inner west could be dogged by similar delay issues that have sparked public anger in Newcastle.

Private company Transit Systems won the tender to operate buses in the Inner West Region Six last week, prompting criticism from the opposition and unions.

The Rail, Tram and Bus Union (RTBU) described the move as a "betrayal" to commuters and drivers, while the opposition is questioning if more regions are slated for privatisation.

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Both have pointed to Newcastle's sharp decline in on-time bus services following recent privatisation as reason to be wary of the change.

The RTBU has cited statistics showing on-time busses dropping from 87 per cent to 52 per cent since a private operator took over in Newcastle.

But Ms Berejiklian said patronage was improving in Newcastle.

"I know for a fact that Newcastle buses used to travel empty, people didn't ride them, the routes were wrong, the service was appalling," Ms Berejiklian told reporters in Sydney on Tuesday.

"Every time we make major change in Newcastle our political opponents complain about it."

Ms Berejiklian said there were teething issues associated with implementing new services but was confident the private operators would iron out any kinks.

"When you move to a new operator, it always takes a while for the service to stand up to what the end product will be, it's always the case," she said.

"On-time running on buses is always lower than other modes of transport, trains and ferries and other modes of public transport aren't subjected to the road conditions."