(Reuters) - Recovery workers in Wisconsin were searching for two missing people on Thursday after an explosion and fire at a corn-milling plant killed at least one person, police said.

Sixteen employees were working at the Didion Milling plant about 80 miles (130 km) northwest of Milwaukee, when the explosion occurred on Wednesday night, according to a press release from the Columbia County Sheriff’s Office.

The sheriff’s office first initially said 16 people had been present at the time of the blast, but later had revised that figure to 17. In a statement later on Thursday the office said 16 was the correct figure.

Eleven people suffered injuries and were transported by helicopter or ambulance to hospitals, the press release said, while two escaped unharmed and two remained missing.

“This is very difficult for everybody that’s been there, including the families that sat for hours waiting for some type of information,” Sheriff Dennis Richards said during a news conference.

Richards declined to name the person who died, and said he did not know the details about the type of injuries sustained by those wounded.

The sheriff’s department and fire department were working with Didion Milling to determine what caused the blast. The investigation is ongoing.

Riley Didion, president of the family-run business that was established some 40 years ago, appeared at the news briefing but offered few details. Didion said it was too early to determine a cause for the explosion.

Along with dry corn mill, the plant also makes ethanol. It was unclear whether the blast occurred in that part of the facility.

(In this version of the story the police corrects official count of number of people in facility to 16, not 17, in paragraphs 2-3 and 11, not 12, injured, in the paragraph four)