Officials are investigating a tank explosion in Toledo, Ohio, that released a chemical into the air, causing a mass evacuation in the area.

One person, a first responder, was injured and taken to the hospital, but officials believe the injuries are non-life threatening. They are also unsure about the cause of the explosion.

An employee at the company, MC Tank Terminal – which specializes in transporting bulk liquid chemicals and provides tank container transportation, storage and maintenance – called on first responders late Tuesday night to address the explosion.

Wade Kapszukiewicz, Toledo’s mayor, announced in a news conference on Wednesday that residents within a 1 mile radius of the explosion needed to evacuate and those within 3 miles were being asked to shelter in place with their windows sealed. He said executives from MC Tank Terminal are en route to Toledo to assess the situation.

“We understand the seriousness of what has happened here,” Kapszukiewicz said. “That’s why we took the actions that we did. That’s why we’re going to continue to monitor and communicate with the public throughout the day.”

The chemical released was glycidyl methacrylate, an industrial coating product used in plastics, rubbers and resins. Local officials say the airborne irritant can cause burning of the eyes, nose, mouth and skin; they have suggested Toledo residents who experience serious symptoms like difficulty breathing, nausea and vomiting, dizziness, or confusion, go to the emergency room or call 911.

When the chemical was released in the explosion, it became a gas, but when it settles back into the tank, it will turn again into a liquid, Kapszukiewicz said at Wednesday’s conference.

“The hope is that at that point, the risk of explosion will have expired, and that efforts can be made to contain and eliminate the hazard,” he said.

Local news outlets in Toledo have reported a visible, dense fog over the town and lurking plastic-like odor.

The city, which has a population of roughly 265,000 people, per the US Census Bureau, had already issued an evacuation order on Tuesday night for about 300 people who live within a half mile of the explosion. That was later expanded to a full mile, evacuating about 1,000 people.

City officials said Wednesday that as far as they know, all residents have been evacuated. Kapszukiewicz said officials are unsure how long the evacuation and shelter orders will last.

Residents are being asked to communicate with local businesses and schools within the evacuation zone to see what their plans are during the evacuation. Some schools were closed Wednesday and others delayed their opening, according to NBC News.