Buckingham Palace confirmed the 97-year-old was behind the wheel of the vehicle when it was involved in the accident with another auto.
According to eyewitnesses, the vehicle that the duke was driving overturned.
Speaking to ITN, Mr Warne said: "Well he was trapped in the vehicle and I told him how to move to free his legs to help get him out".
The palace said the duke was seen later by a doctor as a precaution and confirmed he was not injured.
The prince was checked by a doctor after the accident and determined to be fine, Buckingham Palace said.
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Philip was driving his vehicle at about 3pm, when he pulled out of a driveway onto the A149 in Babingley, Norfolk, just beside Sandringham.
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Prince Philip, 98 in June, had been at the royal estate of Sandringham in rural Norfolk when it occurred on January 17.
As is standard procedure in England in collisions, Norfolk Police performed a breath test for alcohol of the two drivers involved.
The Palace spokeswoman added: 'Contact has been made privately with the occupants in the other auto and well-wishes exchanged'.
An eye-witness contacted the Lynn News soon afterwards to say there were five police cars close to the West Newton turning, with officers combing the undergrowth.
Police said they "are aware of the public interest in this case", but declined Friday to speculate on the cause of the collision.
Following the incident, the 97-year-old Duke expressed concern for the occupants of the Kia, which was also carrying a nine-month-old baby who was uninjured. "I asked him to move his left leg and that freed his right leg and then I helped him get out".
A Downing Street spokeswoman said: "The Prime Minister has sent a private message wishing him well".
He and Elizabeth, 92, have been on an extended Christmas vacation at Sandringham, one of her favored rural homes, located 110 miles (177 kilometers) north of London. "Local police attended the scene".
The Duke, who had successful hip replacement surgery previous year, retired from public life in 2017.