A fire which broke out on Dyffryn Business Park in Ystrad Mynach was deliberate, according to South Wales Fire and Rescue Service.
Police had to close the A469 northbound carriageway between Caerphilly and Ystrad Mynach because of large volumes of smoke.
South Wales Fire and Rescue Service said they received a call at 8.46am on Tuesday May 13 and that crews from Aberbargoed and Caerphilly are at the scene.
At the height of the blaze, four water ladders and two water bowsers were tackling the blaze.
South Wales Fire and Rescue Service said tyres were alight and that the fire had spread to nearby cars and a caravan. Police had to evacuate several surrounding units.
Fire crews had to cut away at a nearby building to stop the fire from spreading.
The fire was extinguished by 1pm.
Environment body Natural Resources Wales also attended the scene.
Emily Roe for Natural Resources Wales said: “Our officers attended the scene of the fire and can reassure local people that no environmental damage of any significance has happened.
“Our biggest concern in incidents such as this is dealing with the water that’s used to fight the blaze. It picks up a lot of pollutants from the burning material and can cause a lot of damage if it gets into streams and rivers.
“However, we’re confident that the vast majority of the firewater used at Ystrad Mynach ran into the foul water drains and therefore poses little risk to the local environment.”
#SWControl Crews are currently dealing with a large fire in Ystrad Mynach involving tyres. Bring your washing in and keep your windows…
— SW Fire & Rescue (@SWFireandRescue) May 13, 2014
#SWControl SWFRS have 4 water ladders & 2 water bowsers dealing with the fire at Ystrad Mynach JE
— SW Fire & Rescue (@SWFireandRescue) May 13, 2014
Are you nearby? Send us your pictures news@caerphilly.observer or text them to 07475099675.
@CaerphillyObsvr pic.twitter.com/o7pB1vY4nO
— Stephen Meades (@meadzy27) May 13, 2014
Update Ystrad Mynach: The fire which is creating large amounts of smoke in the area is involving quantity of tyres which has spread to cars
— Jennie Griffiths (@GriffithsJECtrl) May 13, 2014
Update Ystrad Mynach: On arrival crews from Caerphilly+Aberbargoed asked for a further 2 fire engines and 2 water bowsers to assist
— Jennie Griffiths (@GriffithsJECtrl) May 13, 2014
Update Ystrad Mynach: Fire involving multiple cars and caravan and is also encroaching a building
— Jennie Griffiths (@GriffithsJECtrl) May 13, 2014
Update Ystrad Mynach: due to large volumes of smoke from the fire the Police closed Northbound Carriageway from Caerphilly to Ystrad Mynach
— Jennie Griffiths (@GriffithsJECtrl) May 13, 2014
Update Ystrad Mynach:fire involving 1industrial skip 2motor vehicles 1large caravan+quantity of tyres attempting to stop spread to building
— Jennie Griffiths (@GriffithsJECtrl) May 13, 2014
Update Ystrad Mynach:Crews involved in cutting away fabrication of building adjacent to fire using cutting equipment to check fire spread
— Jennie Griffiths (@GriffithsJECtrl) May 13, 2014
#SWControl The incident at Ystrad Mynach is now being scaled down. 1 water ladder & a water bowser remain in attendance JE
— SW Fire & Rescue (@SWFireandRescue) May 13, 2014