NSW Health Minister Jillian Skinner marked the occasion with a "topping out" ceremony on Tuesday.

Mrs Skinner was flanked by state Liberal candidates for Wollongong, Shellharbour and Keira, as she placed a ribbon around a tree placed atop the structure.

The Scandinavian tradition is said to appease the tree-dwelling spirits displaced during construction.

"It [the car park] complements the $106 million redevelopment of the clinical services block and ambulatory care centre that really is a showcase for a sophisticated redevelopment around a tight site," Mrs Skinner said.

The car park will provide 750 additional spaces next to the existing car park on New Dapto Road.

Once complete, the combined floor area of both car parks will be equivalent to six football fields.

Mrs Skinner described the car park as "an absolutely essential ingredient" to the hospital redevelopment.

She said number of spaces were up on the 638 promised in June 2012 and the structure had been built with "future-proofing" in mind.

"We know that it's highly likely this hospital is going to need to expand in the future, so what they've done is built foundations in this car park and designed it in such a way that future development can go on top of it," she said.

Northern Illawarra Hospitals Group general manager Nicole Sheppard said parking had long been a big issue for staff, patients and their families.

'Kiama MP and government Deputy Whip Gareth Ward described the size of the project as "incredible", with enough rock excavated during construction to fill 14 Olympic-sized swimming pools.

The car park is expected to be finished by June.