An explosion and fire in the South Fork Dairy Farm near Dimmit, Texas, killed 18,000 cows, nearly 90% of their herd. It equals about 20% of the cattle slaughtered in America on any given day. Each cow is worth about $2,000.

The cows were herded together and trapped in pens, waiting to be milked.

One worker was rescued from inside the structure. He is in stable but critical condition.

“It’s mind-boggling,” Dimmitt Mayor Roger Malone said. “I don’t think it’s ever happened before around here. It’s a real tragedy.”

It was the most significant single-incident death of cattle in the country since the Animal Welfare Institute, a Washington-based animal advocacy group, began tracking barn and farm fires in 2013.

People on the scene think a malfunction in a piece of farm equipment may have caused the explosion that led to the fire, said County Judge Mandy Gfeller, the county’s top executive. Texas fire officials are still investigating the cause, she said.

According to BBC, machinery in the facility may have ignited methane gas and the subsequent explosion.

KFDA quoted Sheriff Sal Rivera as saying that the fire might have started with a machine called a “honey badger,” which he described as “vacuum that sucks the manure and water out.”

“Possibly (it) got overheated and probably the methane and things like that ignited and spread out and exploded,” he added.

The dairy opened three years ago and employed about 50 or 60 people.

Mayor Malone said he wasn’t aware of any other fires reported at the facility. He said the dairy had opened in the area just over three years ago and employed 50 to 60 people.

The family who own the farm have not responded to media calls.