Police confirmed on Thursday evening that 60-year-old Francisca Boterhoven De Haan and 59-year-old Canberra lawyer William McCarthy had been in touch via mobile phone and let searchers know they were safe.

"They’ve told us that they’re safe, they’re in good spirits, good health, they have shelter and they are not injured," a spokeswoman for NSW Police said on Thursday evening.

The pair were advised to stay put under shelter and wait out the storms.

"It’s too dangerous to send more people out into the bush," the spokeswoman said.

Searchers will resume their efforts at 7am and expect to extract the hikers from the Ettrema Gorge, where they are located, on foot.

The pair began what was intended to be a three-day bushwalk through the Morton National Park on Saturday, and the alarm was raised on Wednesday when they had failed to return.

Shannon Rogers, Ms Boterhoven De Haan's son, said he spoke to his mum before she left for the hike.

"She was excited about getting in with nature and go swimming in all the waterfalls – she loves swimming and does it everywhere she goes," the 23-year-old said.

"Mum’s an extremely active hiker, she just loves hiking – she’s travelled all over the world hiking and has spent the past three years hiking almost continuously."

Police from the South Coast Police District and SES volunteers began searching the dense bushland of Ettrema Gorge for the pair on Wednesday afternoon, helped by police, ambulance and Westpac helicopters.

About 4pm on Wednesday, Mr McCarthy's car was found in a car park on Tolwong Road in Ettrema, but Inspector Ray Stynes said no other belongings had been found.

The search was suspended overnight and resumed at 7am on Thursday.

Mr Rogers said this was the first time his mum had done the hike but said he believed Mr McCarthy had done it previously.

"I am worried but I’m also very confident in my mum and William who I know is also an experienced outdoor person," he said. "I believe they’re both well ... mum’s either just waiting for the storm to pass or she’s trying to finish the hike as quickly as possible and she’s just unaware that we’re looking for her."

While the weather is not expected to be as bad as last month’s wild storms, Weatherzone said the next few days will experience “extreme weather”.

Inspector Stynes said search coordinators were concerned about the weather, with poor visibility and significant rainfall expected to hit the area over the next 24 hours.

The inspector said bushland in the national park was "fairly thick", making the search difficult.

"It’s a gorge so obviously it's got cliff edges and it’s hard to access," he said.

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