What was supposed to be a relaxed and enjoyable Sunday afternoon trip with friends turned into a horror outing when a 2kg rock smashed through the windscreen of a Penshurst man's Holden Vectra at Berkeley.

The 56-year-old electrical engineer, who wanted to be known only as Mike, had visited the Nan Tien Temple at Berkeley with his wife and two family friends and were on their way to Bowral on the F6 about 1pm when the incident happened.

"I was driving along and then the stone came and hit the windshield and then came inside and hit my forearm first, near the wrist and then came on to my chest," the father of one said.

"I didn't know what had happened and everyone in my car was yelling, 'stop the car, stop the car', but I was afraid that if I did that someone would hit me from behind, so I tried to pull into the shoulder."

Mike said the sound of the rock hitting the car sounded like a gunshot.

"People in my car thought that a bullet must have hit me," he said. "The impact was so huge and was so loud and I was hurting so much. Only when I stopped the car and tried to apply the handbrake did I realise that it was a rock."

Mike went into shock and had difficulty remembering what happened next but his wife, who was in the passenger seat, said she leaned over and put her foot on the brake.

After the car had pulled over, Mike spoke to the driver of another parked vehicle, who was already on the phone to police saying his car had narrowly missed being hit by another thrown rock.

Mike was taken to Wollongong Hospital after the incident and underwent X-rays. He was released later that day with minor injuries to his forearm and bruising on his chest.

Despite narrowly escaping death, Mike had sympathy for the rock throwers, saying he believed they must have come from a disadvantaged background to do such a thing.

"Of course, the first thing, I felt angry, but it really depends on who was throwing the rock," Mike said.

"I know there are quite a few dysfunctional families around and I feel a bit sympathetic towards them if they were kids who did it, because they probably come from a dysfunctional home.

"They should punish them for their deeds, but at the same time it should depend on who they were.

"If they were grown men, then I wouldn't have too much sympathy for them; by that time you should know what you are doing."