IRNA said today it took hours to put out the fire, which began yesterday in Bou Ali Sina petrochemical factory in the southern port of Mahshahr.
It says there were no casualties and that neighboring factories were evacuated as a precaution.
IRNA says investigations are still underway to determine the cause of the fire.
The factory, which is affiliated to Iran's state-owned National Petrochemical Company, opened in 1998.
The area is home to dozens of small and large petrochemical factories, and fires are occasionally reported. Petrochemical products are among Iran's top exports.