A massive operation is underway to repair a critical rail line in the Blue Mountains after a landslide last week will see it closed for a month.

Heavy downpours caused the landslide near Mount Victoria, making a dent that is 40 metres long, 20m wide and 60m deep.

The Minister for Regional Transport, Sam Farraway, said 70 to 100 people were onsite each day as the "absolutely mammoth task" of repairing the "quite significant" damage began.

Repairs will include bringing 40,000 tonnes of rock into the site to re-lay the train tracks and 30,000 tonnes of soil being removed.

Planning is underway to reopen one track from July 24 to allow only the movement of critical freight, and likely only at night.

Full access, including passenger services, are not expected to resume for another four weeks.

Mr Farraway said, while he did not yet know how much this latest round of repairs would cost, crews were well equipped to take on the work following a landslide that developed at Leura after the March wet weather.

"We can't control extreme weather events," he said.

"What we can control is our responsiveness to events and also deploying all the resources we have at our disposal."

Freight delays

The Main Western Line is an important freight route for grains, coal, minerals and meat to cross the Blue Mountains and into Sydney.

One of the largest lamb exporters in the country has had its freight capacity cut in half following the landslide.

Fletchers International Exports at Dubbo in the central west would usually operate four trains a week into Port Botany but could only manage two with disruptions across the entire rail network.

Fletchers International Exports principal Roger Fletcher said it was just another challenge in an incredibly difficult couple of years for freight.

"You know it affects a lot of clients that are expecting product, but you know this is the nature of Australia."

Mr Fletcher said recent slippages on the Newcastle line and a recent derailment near Yass had all combined to create "massive" disruptions throughout the network.

"Transport has had more effect on our customers than anything [recently]."