All four lanes of the new section were officially opened on Sunday morning, just in time for school holiday travellers to arrive.

Parliamentary Secretary for the South Coast Shelley Hancock said with the July school holidays fast approaching, motorists will have a minimum four-lane-highway between Sydney and Jervis Bay Road, south of Nowra.

"It was fantastic to open the first section of the Berry to Bomaderry upgrade this morning to 100 km/h, this is welcome news for tourism along the South Coast with all four lanes open ahead of the upcoming school holidays," Ms Hancock said.

"These upgrades will improve safety, increase road capacity, improve traffic flow and deliver more reliable journeys.

"Locals and visitors are sure to notice the change from what was once a single lane highway with limited overtaking opportunities."

Ms Hancock was joined at the official opening by representatives of Transport for NSW, and project contractor Downer Seymour Whyte.

Minister for Regional Transport and Roads Sam Farraway said the Berry to Bomaderry section is final link in a 30 kilometre upgrade to the Princes Hwy between Gerringong and Bomaderry.

"Since 2012 our Government has been upgrading this stretch of road making it safer for motorists and reducing the bottleneck traffic we see during peak holiday periods," Mr Farraway said.

"Last year we opened the Albion Park Bypass, which was the 'missing link' between Sydney and Bomaderry so the trip down to the South Coast these school holidays is going to be smoother and quicker.

"The new Princes Highway will improve the liveability and productivity of the Illawarra and South Coast region, securing a brighter future for NSW families."

Finishing touches will be added to the stretch of road from October; final asphalt work was affected by wet weather and will resume when the weather warms.

The community will be updated when this work recommences and any changed traffic conditions.

According to the minister, works will be completed by the end of this year.

As part of the upgrade, traffic lights will also be fired up at the Cambewarra Rd/Moss Vale Rd roundabout.

The roundabout will continue to operate as normal, with the traffic lights to activate when traffic volumes are high such as during peak travel times or holiday periods.

For more information visit nswroads.work/berry