The boss of Sydney Trains says there are some disruptions on the network on Monday as the new Hornsby junction comes into action.

The NSW premier has apologised to passengers caught up in last week’s Sydney train chaos and admitted more should have been done ahead of time to prevent the system meltdown.

Almost 40 train services were cancelled ahead of Monday’s morning peak to ensure there wasn’t a repeat of last week’s debacle that left thousands of passengers stranded due to a combination of storms, trackwork, a spike in sick leave and “excess” annual leave approvals.

“With the benefit of hindsight we should have taken proactive action and reduced the number of services that day (Tuesday) and let customers know, so that those delays weren’t experienced,” Gladys Berejiklian told reporters in Sydney after returning to work from her summer holidays.

“I want to wholeheartedly apologise to all of our customers. The system most days is world class and some days, unfortunately, we let commuters down.”

Ms Berejiklian revealed that if “permanent tweaks” were needed to Sydney’s new more intensive train timetable “then we’ll make them”.

The premier insisted, however, there’d be no refunds to commuters inconvenienced last week because there was no “precedent” for that.

The boss of Sydney Trains has assured passengers staff are doing everything possible to keep trains moving on time on Monday.

“I can never guarantee a perfect service but I can assure you my frontline staff, every train driver, every guard is working hard to get people into Sydney today,” chief executive Howard Collins told the Seven Network.

The opening of the new Hornsby junction in the city’s north and the cancellation of trains due to “staff availability” could cause disruptions on the rail network, a Sydney Trains spokesman told AAP on Sunday night.

Sydney Trains cancelled services in advance that were “typically the least busy … ones outside of peak hours or have another train scheduled soon after it”.

Some 36 services were cancelled with buses on hand to supplement reduced services.

Travellers on the busy North Shore line were also warned of a new issue.

“#NorthShoreLine Allow extra travel time from the city due to urgent signal equipment repairs at Milsons Point,” Sydney Trains tweeted after 5am.

The Sydney network went into meltdown early last week with the NSW government blaming drivers calling in sick and storm damage. But it was later revealed management had also approved “excess” annual leave.

Rail bosses met with the Rail, Train and Bus Union on Thursday to discuss the problems ahead of what was termed a “pressure day” on Monday.

“It’s ridiculous that in a city like Sydney we have a timetable that is so poorly designed that it may struggle to get commuters to and home from work on Monday because of these foreseen events,” RTBU NSW secretary Alex Claassens told AAP in a statement.

“We’ve been warning for months that this timetable won’t be able to cope with even minor issues and that the smallest of incidents could send the network into chaos.”

Rail workers on Friday voted to take industrial action as they continue to fight for a six per cent pay rise.

A strike is yet to be confirmed with union delegates and members meeting to discuss what action they’ll take.

– AAP