Transport for NSW has refused to disclose the nature of the "unplanned maintenance" that has thrown the Newcastle Light Rail system into chaos in recent weeks.

Speculation is mounting that operator Keolis Downer is struggling to keep the service running due to continued breakdowns of its light rail fleet.

It follows revelations last year that light rail vehicle 2155 was being used for spare parts to support the remaining five trams.

When the service is operating efficiently, four trams travel between Newcastle Interchange and Newcastle East from 7am to 7pm.

The trams, which controversially replaced the former heavy rail system, are meant to arrive at the light rail stops every 7.5 minutes.

In recent weeks, however, services have been routinely cancelled, leaving hundreds of commuters stranded along the 2.7-kilometre route.

The service has often been running with only two trams.

Information boards advise that trams are running at a 'reduced service'.

On Friday, November 21, the situation became so bad that passengers were advised to catch a replacement bus rather than wait for the light rail.

East End resident Morgan Caldwell caught the light rail between three to four times a week.

However, Mr Caldwell said the service had become virtually redundant in recent weeks due to the frequent cancellations.

"When it is working it's really good but lately it's just bullshit," he said.

"You turn up at the station and see all of the cancelled services. It's quicker to walk."

"A lot of people are talking about how bad it is. I really feel for older people and those who don't have cars and are completely dependent on it."

Transport for NSW responded to a Newcastle Herald inquiry about the cancellations sent to Keolis Downer.

A spokeswoman confirmed light rail services were operating at a "reduced capacity due to unplanned maintenance" that had impacted service reliability this month.

"Maintenance work is being prioritised to return services to normal as soon as possible," she said.

"In the meantime, weekday peak frequency- normally every 7.5 minutes between 7am and 7pm - is being temporarily affected," she said.

Transport for NSW did not provide details of the unplanned maintenance or how many services had been cancelled in recent months.

It said: "So far in November, 92.3 per cent of light rail services have run as scheduled. In October, 99.6 per cent of services ran as scheduled."

Several sources have told the Herald that the light rail pantographs (the trams' charging bars) and onboard energy storage systems experience problems on a regular basis.

Transport for NSW declined to comment on this issue, or on whether there were plans to return light rail vehicle 2155 to service.

The Herald has previously reported that chassis cracking has been detected in all six Newcastle light rail vehicles but was not considered serious enough to warrant repairs.

The Transport for NSW spokeswoman said that Keolis Downer was working to restore service reliability as quickly as possible.

"We apologise for the inconvenience caused to passengers at this time," she said.

"The operator is keeping passengers informed about service disruptions via updates to Trip Planner, travel apps and public information displays at light rail stops along with public announcements where available.

"Where there is minimal notice to update the customer information apps, customer service staff are being deployed to light rail platforms and Newcastle Interchange to direct passengers to alternative services."