"Apparently the SUV had clipped a couple of other vehicles before hitting the tree."
James, 33, from Te Atatu, said her nursing instincts kicked into action and she pulled over to help.
"The man, who I believe lives locally, was unconscious behind the wheel and no one really knew what to do," she said. "I asked people to let me through because I was a nurse and I saw the man was in a really bad way.
"I couldn't find a pulse so I started doing CPR but didn't think it would work.
"Fortunately another nurse pulled up and started to help too as I was getting really tired. The patient was a really big dude in his 60s and it took a few people to even get him out of the car.
"We could only do our best until an ambulance arrived but I didn't think he would make it."
James was surprised when police contacted her to say the man's wife wanted to pass on her thanks for saving her hubby.
"She said he was doing well in hospital and needed heart surgery. I am very keen to meet them both and see how he is doing in person."
James joined Shortland Street as a story table medical advisor three years ago before becoming a scriptwriter.
She said the experience had got her thinking about a storyline to raise awareness about the importance of learning how to perform CPR.
"Few people know how to do it but it can be a really important skill to have in an emergency situation."
It is the second time this year someone from Shortland Street has become an off-screen hero.
Pua Magasiva, who plays Vinnie Kruse on the soap, last month helped pull a man from a burning car wreck, after the vehicle smashed into a tree north of Auckland.
"The car was on fire, so we were trying to get him out as quick as we could because - you never know - it could've blown up," Pua Magasiva told the Herald.
Police praised members of the public, including Magasiva, who helped to free the man after the crash on the Hibiscus Coast Highway .They say they saved the man's life.