"I was driving home and I saw a vehicle, a black (Land) Rover come out from a side road and it rolled", witness Roy Warne told BBC Radio on Friday.
The duke appeared to be travelling without a police protection officer, individuals who guard all senior members of the Royal Family when at public and private events.
The average speed camera system would cover the A149 from the junction with the A148, around two-and-a-half miles south of the crash scene.
He walked away without serious injuries but witnesses said he was lucky to escape alive.
The Queen has been in the auto in the past while her husband was involved in accidents, including in June 1964, when 32-year-old machinist Henry Cooper was driving to the Rising Sun public house at Holyport, near Madienhead, in his '89 Ford Popular.
Norfolk Police said two women - the 28-year-old Kia driver, who suffered cuts to her knee, and a 45-year-old passenger who broke a wrist - were treated at the local Queen Elizabeth Hospital in King's Lynn that day and discharged.
Local police told CTV News that Prince Philip and the female driver of the other vehicle were both breathalyzed and both tested negative.
Cobb and his teenage daughter were driving past when they saw the accident about 100 yards from their home.
It involved a Kia auto carrying two women, who were treated for minor injuries, and a baby, who was unhurt.
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Two people in the other vehicle were injured and taken to the hospital.
A first responder at the scene said the Duke of Edinburgh cried out "my legs" as he was pulled from the wreckage.
"I helped him move his legs which were a little trapped and a bit crushed, then I saw his face and I realized who it was", Warne said.
An eyewitness to the crash, Roy Warne, said that the royal seemed "shaken" after his accident, but was uninjured.
Philip, who retired from public duties in the summer of 2017 and last April had a hip replacement operation, is known to remain active.
The Palace confirmed that Philip wasn't injured in the collision.
Seward added: "And I'm sure she'll be very annoyed with him this morning - obviously sympathetic - but she will be saying 'now Philip this is enough, you've got to stop driving'".
The Queen has never had to do a driving test and is the only person in Britain allowed to sit behind the wheel without a licence.
He was photographed in the summer driving a horse-drawn carriage, although he has given up competing.
Drivers in the United Kingdom aged 70 and above need to reapply for their license every three years, for which there is a mandatory eyesight test.