The landslip has reduced the highway - one of two major routes over the Blue Mountains - to a one lane road, with alternating stop-slow conditions remaining in place through the westbound carriageway.

The incident occurred at around 6.30pm on Thursday evening between Victoria Falls Road and Harley Avenue, with emergency services and crews from Transport for NSW immediately attending and remaining on site.

As of 7am emergency services and Transport for NSW were reportedly still on site to the limited traffic flow around the area, with significant delays still expected, particularly during peak periods.

If unable to avoid the area motorists are advised to allow plenty of extra travel time.

The incident has the potential to wreak havoc on through the Blue Mountains again, as was seen over the Easter long weekend when Bells Line of Road remained closed due to landslips near Mount Tomah.

Significant logjams were created throughout that weekend, with queues on the Great Western Highway at one stage stretching for kilometres as that road was also impacted, albeit less.

With changed road conditions still in place on Bells Line of Road as a result of those landslips, motorists are advised to plan well ahead before travelling on Friday, or later in the weekend.

On Bells Line of Road, through the Mount Tomah area, a reduced speed limit remains in place with portable traffic signals allowing motorists to pass in one direction at a time near the Blue Mountains Botancial Gardens.

Transport for NSW is continuing to monitor Bells Line of Rd however, slopes will be susceptible to future weather events that may result in planned or unplanned closures.

Motorists are also advised to check Live Traffic for updates on both routes, or call the NSW Transport Management Centre on 132 701.

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