The Newcastle Herald understands the long-awaited introduction of the $2 billion fleet, which is replacing the decades-old V-set trains, has been set back even longer due to delays training staff.

The trains are already a year late coming into service. The NSW government initially planned to begin passenger services in late 2019, but the first trains of the 55 ordered did not arrive from South Korea until December.

A row with the Rail, Tram and Bus Union over how the trains operate, which the union says is not resolved, has also hampered the rollout.

"The great Korean train debacle has been a mess from the beginning," the Opposition's transport spokesman Chris Minns said.

"Commuters and the Parliament have been kept in the dark as to when these trains will ever hit the tracks."

Regional Transport Minister Paul Toole said earlier this month the trains would be rolled out "later this year", but sources say driver and guard training has not progressed as hoped and that timeline is unlikely to be met.

Transport for NSW conceded in a statement on Friday that the training program was "being refined" after pilot courses and NSW TrainLink staff were yet to progress beyond simulators.

"Whilst our plan is still to have the first train servicing customers on the Newcastle and Central Coast line before the end of the year, [it] is dependent on successful completion of testing," it said.

Four trains have been in testing for months. One reached Wickham for the first time in June and trains also travelled into the service centre at Kangy Angy for the first time earlier this month.

The trains are due to run on the Central Coast-Newcastle line first, before the Blue Mountains and South Coast.

RTBU NSW Secretary Alex Claassens said the union had effectively been kept in the dark about the fleet's rollout.

"The entire process of importing and testing the New Intercity Fleet has been hidden from scrutiny, with Transport for NSW ... forcing everyone who has access to the [trains] to sign non-disclosure agreements," he said.

Members still have concerns about the operating model, Mr Claassens said, despite a government-ordered report declaring it "safer than comparable rail operations around the world".

"98 per cent of train workers the union surveyed said they would refuse to staff these trains until their safety concerns were addressed."

Newcastle state MP Tim Crakanthorp said the government talked "a big game" about transport projects but "consistently" failed "to deliver on time or on budget".

"I might ask Santa to bring Newcastle one of these trains; at least we know his delivery date," he said.

"It's been problem after problem with this fleet, and unfortunately this government has given us no reason to have faith that these trains will be on our tracks soon."

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