South Yorkshire Fire and Rescue were sent out to the car blaze on Church Street, Thorne at around 1.30am.
A spokesman said: "A witness said they saw someone throw a petrol bomb.
"The incident has now been left with the police."
Arsonist threw 'petrol bomb' at car on Doncaster street
Firefighters were called out to extinguish a car fire on a Doncaster street in the early hours of this morning, amid witness reports that the blaze was started using a petrol bomb.