Paige Davis felt unsafe and demanded to get out of a car that she considered was being driven dangerously.
Less than a minute later, the car was teetering down a bank, the remaining two occupants trapped inside.
Davis, 18, said they were lucky to be alive.
Emergency services were called to Leith Valley Rd, in Dunedin, after reports of a car leaving the road at 12.45pm yesterday.
It was Davis who called police.
She said she had been in the car with another young woman and a man when she asked to be let out because she felt the manner of driving was unsafe.
She described it as "drifting and rallying" on the gravel road.
After the other occupants initially tried to convince her to stay, the driver pulled over and she got out.
Less than a minute later, she heard the crash.
She raced to the bank where she saw the car about 4m down, resting above a creek.
She could not get down to them, and she could not get either of them to respond to her.
"I thought they were dead."
Emergency services arrived, and firefighters were able to extract the pair and help them up the bank using a rope.
A St John spokesman said two people were assessed at the scene and found to have minor injuries.
Davis reflected on her decision to leave the car.
"I can't believe I got out at the right time."
The incident came just days after a warning from police about dangerous driving and racing in Dunedin.
Senior Constable Steve Tvrdeic said it appeared the young female driver had lost control on the road and the vehicle had gone over the bank.
"They were quite lucky. I think if they would have tried to get out the car could have dislodged and continued down into the creek."
He was still working to establish whether there was any driving behaviour that led to the crash.
The car would probably be written off, he said.