"Buses are replacing NSW TrainLink services between Katoomba and Mt Victoria on the Blue Mountains lines due to the landslip on the western rail line near Blackheath," the spokesperson said.

"Services on the Blue Mountains line through to Dubbo/Broken Hill and Bathurst will be affected for several weeks while repairs are made to the line.

"Some scheduled replacement services may not have appeared in the Transport for NSW Trip Planner timetable and Transport is currently working on rectifying the timetable information for customers."

TfNSW said customers should anticipate amended timetables, allow plenty of extra travel time and plan ahead using the transport apps or visit www.transportnsw.info/regional.

The Dubbo XPT to Sydney will be affected for what may be weeks due to a landslip near Blackheath.

Minister for Regional Transport Sam Farraway said on Tuesday afternoon that the recent wild weather in the Blue Mountains had caused what he described as a "major landslip" to develop overnight alongside the main western rail line across the Blue Mountains.

He said it would take weeks to repair.

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"The landslip, which occurred near Blackheath, has closed the line between Katoomba and Mount Victoria, which means passenger services and freight cannot travel over the Blue Mountains," Mr Farraway said.

"Crews are onsite, including geotechnical engineers, to understand the full impacts of the landslip.

"Initial inspections indicate the landslip that has developed is 40 metres long, 20 metres wide and up to 60 metres deep.

"Maintenance crews will work actively to restore full access to the line, undertaking track and other associated infrastructure repairs, once it is safe to do so. Safety is the top priority."

Mr Farraway said Transport for NSW was "working closely with the freight industry to communicate the impacts and find viable alternatives to move goods and supplies".

He said the Dubbo and Broken Hill XPT services to and from Sydney had been replaced by coaches, where available.

"For customers travelling to and from Blue Mountains Line stations, you will need to catch T1 Western Line services between Central and Penrith," he said.

"Please avoid all non-essential travel. If you need to travel, plan ahead using the transport apps and transportnsw.info for updates or use other transport options."

Separately, those who had been planning to travel to Sydney by car by the Bells Line of Road have been told they will have to detour along the Great Western Highway until floodwater recedes on the bridge at North Richmond.

Transport for NSW says variable message signs are in place en-route and motorists are advised to follow the diversions as directed.

"Motorists are advised to allow additional travel time, drive to the conditions and follow the direction of signs and traffic control," a Transport for NSW spokesperson said.

"If possible, motorists should delay non-essential travel and avoid the area.

"Transport for NSW thanks motorists for their patience during this time."

For the latest traffic updates download the Live Traffic NSW App, visit livetraffic.com or call 132 701.