The current order of 55 engines and 554 carriages to service the Illawarra, Newcastle, Central Coast and Blue Mountains was originally scheduled to begin arriving in March 2019.

But on Monday it was reported the first trains won't land until later this year, meaning they won't roll out until 2020.

Mr Constance said the government was working through local industrial disputes and design issues.

Projected to cost $2.43 billion, the new intercity fleet is set to replace the V set trains which have been in service for more than 40 years.

"There are ongoing industrial issues in relation to the design of the train being worked through (but) my expectation is we'll see a train arrive later this year," Mr Constance told reporters.

"We're just getting on with the job and at the same time expect Transport for NSW and the (Rail Tram and Bus Union) can work through the issues.

"No one is rushing the testing or commissioning of any train and that is my expectation. I don't care if takes a bit longer, it's got to be done with safety first."

The union on Monday again said a design fault in the new trains meant guards could not properly monitor passengers as they boarded.

It wants the order delayed until safety concerns are addressed.

"It needs to be changed or we risk serious injuries or worse on the network," RTBU state secretary Alex Claassens said.

The construction and maintenance contract for the new fleet was secured in 2016 by a consortium made up of Australian engineering firm UGL Limited, Mitsubishi Electric Australia and Korea's Hyundai Rotem Company.

Maintenance will take place at a new facility on the Central Coast.

Australian Associated Press