Firefighters are tackling a blaze of about 20 hay bales in a field at Swinton.
South Yorkshire Fire Service was alerted to the fire, in a field off Wentworth Road at Swinton before 2pm today.
A spokesman said: “No properties are at risk. The fire is in the middle of a field and is thought to have been started deliberately.
“The crew is breaking up the bales to gain full control and is expected to be there for a while yet.”