Pictures posted to social media show the large rocks blocking both lanes of the highway on Brown Mountain before 5pm on February 15, after becoming dislodged.

The area is known for its granite tors, or outcrops, which can move when rain falls on the soft clay and sand soil, which is formed from the breakdown over time of minerals in the granite, and exposed during the making of the road to Piper's Lookout.

In 2016, one lane of the highway at Brown Mountain was closed due to a landslide, and in 2012 questions were raised over whether heavy vehicles should be using the road after heavy rain caused a landslide.

Australian-owned and Jindabyne-based drill and blast company Rock Breaking Solutions said the conditions on Saturday night were too risky to attempt to clear the rocks, which they said weighed around 40 tonnes and 80 tonnes.

"They couldn't have fallen any better, but the guard rail was completely shot," managing director Deon Becker said.

The team returned on Sunday morning to clear the road, destroying the smaller of the two rocks at around 9am, and the larger rock at 12pm.

The company used a non-explosive technique, which uses pressure created by expanding gas from inside a capsule, to break stone and concrete. The technique is used in environmentally sensitive areas, Mr Becker said.

A wheel mounted remote controlled drill rig was used to make the hole in the large granite rock, before a NoneX Low impact rock breaking cartridge was placed inside.

Mr Becker said the NSW Roads and Maritime Service and contractor RD Miller Earthmoving and Excavations assessed the road before it was reopened at around 3.30pm on Sunday.

Transport for NSW said the remaining debris was then transported to one of its existing stockpile sites.

"The highway was closed for around 24 hours to allow crews to clear the road and assess the site," a Transport for NSW spokesperson said.

"A number of other sites on Brown Mountain were also inspected by Transport for New South Wales geotechnical experts before the road reopened.

"Transport for New South Wales carries out regular inspections on the highway at Brown Mountain and currently is planning for a number of slope stabilisation projects to be carried out in the next three to five years."

The Bega Valley branch of the NSW State Emergency Service has also been working to clear roads across the region alongside other agencies and contractors.

"The rains moved huge amounts of sediment, caused scores of new trees to topple, and created landslides causing additional damage to infrastructure," they said over the weekend.

"Between the damage cause by bushfires and now flooding rains, some of our amazing south coast landscape will take many years to recover.

"Countless tree arborists, machine operators, truck drivers, labourers, tree assessors, road workers, engineers, field staff and traffic controllers are all working to get things safe for the public."