9News understands the nuns had returned from a day trip to the Schoenstatt Sisters of Mary Institute on Fairlight Road in Mulgoa, when the driver hit the accelerator instead of the brake.

An 83-year-old passenger was airlifted to Westmead Hospital in a critical condition.

The driver and four other women were treated for a range of bumps and bruises in the car park.

NSW ambulance inspector Nathan Sheraton said it was very fortunate the car was stopped by a tree stump.

"Divine intervention was definitely involved here," Sheraton said.

Kathryn from the Schoenstatt Sisters of Mary Institute said one sister remained in hospital in intensive care while the others recovered at home this morning.

"These women are pioneers, they came to Australia as missionaries a lot of them," Kathryn said.

"Now it is their time to have some peace, understand and compassion from the community at large."

Many of the nuns came from Germany to serve a life of devotion under the Roman Catholic Church.