An explosion has occurred in a slag pit in northwestern Indiana.

The blast at Lafarge North America in East Chicago Sunday afternoon was at a contractor's facility at a mill that turns slag into cement, the (Northwest Indiana) Times reported.

No injuries were reported, said Patricia Persico, a spokeswoman for Cleveland-Cliffs Indiana Harbor West.

The explosion was in the raw materials section of the mill along Lake Michigan. Several small fires at the mill had to be extinguished.

Slag is a highly volatile byproduct of steelmaking prone to exploding when mixed with water, according to the newspaper.

Persico said recent rain caused the explosion.