Whanganui Fire and Emergency senior station officer Jes Sorensen said the blaze was extinguished quickly.
"I believe the car had been involved in an accident earlier in the day.
'I can't comment on what caused the fire as I believe the police are investigating."
Police confirmed that SH3 was blocked for a short time until the fire was out. The car was then taken away.
"The car had been involved in a collision at around 6.45am on Saturday," a spokesperson said.
Whanganui police also attended a car crash in Castlecliff near the corner of Mosston Rd and Puriri St at 10.30am on Saturday.
The police spokesperson said one driver was taken to hospital with a shoulder injury.
"Police spoke to witnesses and will be making further investigations."