Police responded to the car being trapped in floodwaters on Cattai Ridge Road about 6.25am on Wednesday.

The vehicle was found after 1pm with the man's body inside.

Detective Inspector Chris Laird later said the 25-year-old was in a newly-hired Toyota Camry vehicle and was on his first day of a new contracting job.

Det Insp Laird told reporters the man had called triple zero when he hit water and began to sink, and remained on the line with the operator until about 7am.

He said the roads had multiple signs and road closure warnings, yet the car was located 30 metres into flood waters and six metres under water.

There was also a padlocked gate blocking off the road, but it was submerged.

Det Insp Laird suggested the car's electrical system may have failed.

"We can only speculate as to why he couldn't get out of the car and initial examination shows he made all reasonable attempts," he told reporters.

"Also too, the remote location of the area, (we'll ask) questions about what he was doing up there ... he may not have known the area as locals would."

Det Insp Laird said the 25-year-old had strong roots in western Sydney, and that his friends in Australia were devastated by the news.

"From the police force, all emergency services ... here is the very reason why you should not make any attempt to drive through swollen rivers," he said.

Premier Gladys Berejiklian expressed her condolences to the man's family.

Emergency Services Minister David Elliott also offered his condolences, saying it would send ripples through the northwest Sydney community.

"The human cost of these floods has been brought into sharp focus in the most tragic of circumstances and I urge communities to continue to be cautious in the face of continued and imminent threats to life," Mr Elliott said.

Prime Minister Scott Morrison and Opposition Leader Anthony Albanese also made statements in federal parliament commemorating the 25-year-old.

Mr Morrison labelled Wednesday a "terribly sad day", saying he knew the area well from childhood camping trips and empathising with the man's family.

He thanked NSW emergency services for their work.

"We have seen so much over the course of the past year and more as this country has battled so many things - floods, fires, viruses, drought and now these floods again," Mr Morrison said on Wednesday.

"Now this family will get this news and they will grieve.

"Around them, activity will occur as the flood waters recede and the clean up begins, but their house will be dark and their grief will be great."

Queensland subsequently recorded its first flood death on Wednesday when a man's body was found in his submerged ute near the Gold Coast.

Australian Associated Press