Urgent work is underway to restore train services to their regular timetable ahead of afternoon peak hour after a snapped cable caused massive delays.

While trains are running again, passengers travelling on the T1 North Shore and Central Coast Newcastle Line may continue to experience delays and flow-on impacts as they travel home this afternoon, Transport for NSW said.

Passengers should also allow extra travel time on the T4 Eastern Suburbs and Illawarra Line following an incident requiring emergency services at Central.

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Thousands of commuters had their morning commutes impacted after an overhead cable snapped between Chatswood and Artarmon stations in North Sydney early on Tuesday.

WATCH THE VIDEO ABOVE: Overhead wire collapse causes Sydney train chaos

Transport NSW said the issue ”necessitated urgent repairs to the overhead wiring at Chatswood Station, which halted all city-bound trains on Tuesday morning”.

The urgent repairs caused city-bound trains on the T1 North Shore Line to be replaced by buses between Gordon and Chatswood, while trains along the T9 Northern Line were also impacted.

One commuter said the delays caused a number of people to become “packed on the Metro line”.

“There’s people actually pushing in, squeezing into the carriages, which is not very pleasant,” they said.

Sydney Trains CEO Matt Longland apologised to commuters who were hit with the delays but noted the “power line issue has now been repaired”.

“The line’s been re-energised and we are now operating services again on the T1 and the T9 line,” Longland said.

Transport for NSW said said passengers may experience some residual delays this afternoon as trains and crew are repositioned and the timetable is restored across the network.

Sydney Trains CEO Matt Longland said officials are trying to restore services to their standard timetables before the after-work rush. Credit: 7NEWS

“We’ve got two hours before the PM peak starts and that’s our priority at the moment,” Longland said at 1pm.

“We’ve got additional staff that we’ve called in, additional train crew and also additional staff at stations to assist passengers.

“So for anybody travelling this afternoon, our advice is that they should plan for a normal timetable to be operating across all lines.

“However, keep an eye on social media ... for any incidents or any updates over the next few hours.”