Cell phone video shows a 79-year-old man being ripped from his car as it nosedives into the Merrimack River.
Witnesses said a stranger jumped in the water to pull the driver to safety.
"The car was under," said Joe Grande of Metheun. "I mean, he was extremely lucky that there was someone here if not, it would be a different story."
It happened Sunday afternoon in Cashman Park.
Newburyport Police said the driver accidentally hit the gas instead of the brake sending the car over the curb, down the rocks and into the water.
"[The driver] said when he got in he tried to open the door," said Jack Cameron of Amesbury. "He said, 'Oh yeah. I couldn't get out.' Luckily for him, his window was down."
Moments after the rescue, the roof was barely visible as it bobbed in the water.
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"The were a lot of people down here and again, everyone thought he was still in the water," said Suzanne Ritter of Salisbury. "A lot of people thought it was still in there when we pulled up."
Police said the driver, who refused medical treatment, is okay.