The delivery of NSW's multibillion-dollar fleet of new intercity trains from South Korea is running late, which risks delaying the start of their first passenger services until the first half of next year.

The first of the trains to roll off the assembly line had initially been expected to arrive by ship in March but they are now unlikely to be delivered until November or December.

The trains will have to undergo three to four months of testing after they arrive, which means the original plan to press them into regular passenger services on the rail line from Sydney to the Central Coast and Newcastle late this year is unlikely to be realised.

Transport Minister Andrew Constance in front of a mock of one of the new intercity trains. Credit:Janie Barrett

Construction of a $265 million maintenance facility for the intercity trains at Kangy Angy on the Central Coast is also running late due to factors such as multiple design changes.