An apparent explosion sparked a fire at a massive Quaker Oats plant in Iowa on Saturday, sending thick black smoke billowing over downtown Cedar Rapids as firefighters rushed to the facility billed as the world’s largest oat mill.

No injuries were reported, and all workers were safely accounted for, according to local officials.

The Quaker Oats plant is the world’s largest milling facility, processing more than 2 million pounds of oats each day, according to the company’s website.

Firefighters were called to the plant at around 4:44 p.m. local time after reports of an explosion and fire, according to the Cedar Rapids Fire Department. When crews arrived, they found heavy smoke and flames coming from the north side of the building.

Additional firefighters from Marion, Hiawatha and Linn County were called in to help battle the blaze.

Cedar Rapids Mayor Tiffany O’Donnell said in a Facebook video that all workers were safe and accounted for. She said the fire broke out in an area of the plant where relatively few employees were working.

“It’s not heavily populated with employees and team members. Which, of course, in this case was a blessing,” O’Donnell said.

Most of the fire had been put out by 6:25 p.m., though firefighters were still working inside the building, the fire department said.

No firefighters were injured.

Authorities have not said what caused the explosion or how much damage the fire caused.

PepsiCo Foods US, which owns Quaker Oats, said the cause of the fire would be investigated.