The Great Western Highway will remain closed at Victoria Pass for at least three months.

A major geotechnical failure at Mitchell's Causeway has made the road unsafe, the NSW Government says, announcing they'll ensure extra rail, coach and bus services to support Blue Mountains and Central West communities.

Minister for Roads and Regional Transport Jenny Aitchison said she understood this was difficult news, "but people deserve honesty and they deserve clarity".

“I will be honest and upfront to the people of the Blue Mountains and the Central West: this closure is expected to remain in place for at least three months – it is incredibly serious," Ms Aitchison said.

“This is not a short-term repair job. We are dealing with a major geotechnical failure on a fragile and historic section of road, and it must be assessed and repaired properly.

“We are rolling out extra rail, coach and bus services now because communities need practical support, not just advice.

“I know this closure is causing real hardship for families, workers, school communities, freight operators and local businesses, and I am deeply sorry for that disruption.

“But there will be no shortcuts on safety – we will not risk lives."

The 194-year-old Mitchell’s Causeway, also known as the Convict Bridge, has been closed in both directions since Sunday 8 March, after proactive monitoring by Transport for NSW detected significant cracking and movement in the substructure.

Some 90 staff, including specialist engineers, maintenance workers and operational crews, have been working around the clock.

Transport for NSW has advised that at least two weeks of specialist geotechnical testing and 3D imaging must be carried out with no passing traffic to understand the full extent of the damage.

Even under the most optimistic scenario, any remediation required to make the road safe for vehicles would take at least a further two months.

 Transport for NSW will:

From Sunday, 15 March, Sydney Trains has committed to providing additional services between Bathurst and Mount Victoria, with timetable details being worked through

From Saturday, 14 March, provide two fully accessible coaches to run 12 daily NSW TrainLink services between Bathurst and Katoomba – six in each direction. These free turn-up-and-go services will stop at Katoomba, Mount Victoria, Lithgow and Bathurst stations

From Friday, 13 March, run amended school and regular route bus services operated by Lithgow Buslines to help reduce journey times for students on routes affected by the highway closure

Boost resilience of road along Bells Line of Road and Darling Causeway to reduce traffic impacts and preserve road quality

For NRL fans attending Saturday night’s early season Sharks v Panthers game at Carrington Park, Bathurst – there are still more than 100 tickets available on the XPT from Central to Bathurst on Saturday and returning Sunday.

An incident management team has been established to coordinate with other government agencies, local councils, freight operators, the National Heavy Vehicle Regulator and other affected stakeholders.

Bells Line of Road will continue to carry most detoured traffic from the Great Western Highway.

Motorists are urged to consider alternative long-distance routes, including the Hume Highway or Golden Highway, or alternate modes of transport where suitable.

The alternate route via Darling Causeway to Bells Line of Road is typically adding up to 25 minutes to a crossing of the Blue Mountains, but motorists should expect heavier traffic and delays, particularly during peak periods and on weekends.

Traffic control points remain staffed across the Mountains and may temporarily stop general traffic to allow critical movements by emergency vehicles and essential health staff.

 Transport for NSW Deputy Secretary, Road Maintenance and Resilience, Matt Fuller said Transport would continue to monitor strategies and adapt where they can to meet the needs of passengers, motorists and road users.

“This is a complex site, with a unique heritage structure on a mountain pass and the level of movement detected means we need time without traffic to fully understand the risks and determine the safest solution," Mr Fuller said.

“Drivers should plan ahead and expect delays on alternate routes, particularly during peak periods and on weekends. We ask people to drive to conditions and be patient and respectful of others on the road.”