Commuters in Sydney have been warned of delays on several train lines due to urgent repairs.

Issues with signals at Circular Quay and Town Hall stations were noticed overnight, with repairs beginning on Monday morning.

Passengers on the Leppington and Inner West, Liverpool and Inner West, and Airport and South lines have been urged to allow for up to 50 minutes of extra travel time.

“Trains continue to run however there may be larger than normal gaps between services, trains may stop on platforms for longer than usual and train stopping patterns may change,” Transport NSW said.

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“Passengers should also listen to announcements and check information displays for service updates.”

An update on the agency’s website says repairs are “expected to be completed by 8.30am”.