More than half a million rail commuters will be forced to catch buses on weekends for at least a year as the Sydney network undergoes a major maintenance blitz.

Close to 4,000 repairs, upgrades and refurbishments to equipment, including tracks and signalling systems started this weekend at a cost of about $97 million — impacting about 600,000 passengers.

The "biggest co-ordinated program ever" is in response to an expert review of the rail service that found it was plagued by a backlog of almost 40,000 defects. 

NSW Transport Minister Jo Haylen said years of neglect had created a sub-standard network, with the millions of people who rely on trains "losing faith in the system." 

"We have to fix our rail network and it's going to take a massive effort," she said.

"The work will be around the clock from midnight Friday to midnight Sunday.

"It's a year or more of pain but it will deliver the huge, world-class train system Sydney needs and deserves."

Hundreds of workers on location at about 100 sites are expected to repair about 450 kilometres of rail.

More than 14,000 maintenance shifts have been allocated to the project, with 1,900 defects taking priority.

Last month, the Sydney Trains Review panel released its interim report detailing how extreme weather events, industrial action and the introduction of a new timetable in 2017 had caused repairs to be delayed or not undertaken.

The consequences for commuters were dire. Disruptions reached their peak in March, with three events — including a critical communications failure — leaving thousands stranded for hours.

Today's Sydney Rail Repair Plan announcement is in line with the 12 recommendations contained in the interim report, according to Ms Haylen, and is a step towards restoring reliability in the system.

She says continuing system failures and meltdowns are not an option.

Opposition Leader Mark Speakman said the works only represented 7 per cent of the total maintenance budget. 

"This is a massive PR stunt by the Labor government," he said. 

"This is not some kind of transformational project by the Labor government." 

He blamed the maintenance backlog on the unions. 

Commuters at Sydney's Central Station told the ABC they were frustrated with the state of the rail system. 

"The problem is just that you can't rely on public transport," one commuter said.

"Something definitely needs to be improved."

Another expressed concern at buses replacing trains for the duration of the maintenance work.

"I get it, we are trying to get better trains, but at the same time, buses aren't always accurate or on time."