Firefighters dealt with a spate of car blazes in one night.
The first involved a Lexus, which caught fire near Ulley Reservoir on Pleasley Road, Rotherham, at 7.30pm on Tuesday.
An hour later, a Peugeot 206 went up in flames on Jenkin Road, Wincobank, Sheffield.
Both fires are believed to have started accidentally.
The next two incidents crews were called out to were arson attacks.
The first was a Ford Transporter van which was set alight on Hollytree Avenue, Maltby, Rotherham, at 12.50am yesterday and the second was a Peugeot 106 which was fired on Harvis Lane, Shalesmoor, at 5am.
n Witnesses to the arson attacks or anyone with information on those responsible should call police on 101.