Raymond, the schools superintendent, said his district plans to have counselors on hand when students return Friday.
There were multiple burn injuries reported at the Didion Milling plant in Cambria, officials told WKOW-TV.
According to OSHA records uncovered by WISCTV News 3 reporter Chris Gothner, Didion Milling had previously been cited for "serious" safety violations as recently as 2011. The AP says Didion officials did not immediately respond to messages seeking comment about the explosion.
Williams said the mill processes corn and corn by-products for ethanol plants.
Williams said multiple fire departments and more than four medical helicopters were called to the scene, but he did not know how many people were injured or the extent of the injuries. The Associated Press is reporting that OSHA cited the plant six years ago, because workers were exposed to explosion and fire hazards.
The blast leveled the corn milling structure at the Didion complex in Columbia, a village of about 770 residents roughly 45 miles northeast of Madison.More news: June 8 Poll: Theresa May Defends UK Political Debate Boycott
The University of Wisconsin Hospital in Madison received five people injured in the blast, but hospital spokeswoman Emily Kumlien said patient privacy laws prevented her from releasing any information on their conditions.
The village was not evacuated and Williams said he was told there was no further threat.
Cambria Village Clerk/Treasurer Lois Frank told the local newspaper, the Daily Citizen, "We heard a loud boom and the house shook".
The incident was reported late Wednesday night at the Didion Milling plant on Highway 146 in Cambria.
The company employs more than 200 people.