Crews from Cannock, Cheadle, Lichfield and Rising Brook were called to reports of the fire on a field on Thorneyfields Lane near Stafford on Friday afternoon at around 2pm.
They arrived to find an area of 200 metres by 300 metres well alight and used six pumps and four hose reel jets to extinguish the fire.
No injuries were reported and fire fighters remained at the scene afterwards.
A spokesman for Staffordshire Fire and Rescue said: "Firefighters are currently tackling a large hay bay fire in the Stafford area.
"Crews were called to a field on Thorneyfields Lane at 2pm this afternoon (Friday 12 August).
"Firefighters from Cannock, Cheadle, Lichfield and Rising Brook attended the scene.
"Upon arrival, crews found an area of 200m by 300m well alight.
"No one has been reported injured.
"Crews are using six pumps and four hose reel jets to extinguish the fire.
"Firefighters remain at the scene."