NORTHWOOD — Four people are being treated at Mercy Medical Center-North Iowa after a chemical fire this morning caused all of Northwood to evacuate.

A hospital spokeswoman said the extent of their injuries is unknown.

People with symptoms including vomiting, nausea or respiratory issues are asked to go to the hospital, she said.

Initial reports indicate the fire is at a fertilizer storage facility at the airport on the east side of town. There are reports of sulfuric acid contamination.

How the fire began remains unclear.

A shelter is set up at the Kensett Community Center, about 6.5 miles south of Northwood, and residents with pets have been asked to go to Kensett City Hall. At about 10:30 a.m., there were about 200 people at the community center and about 25 at City Hall.

Steve O’Neil, Cerro Gordo County emergency management director, said the community center was reaching capacity, and he anticipated another shelter to be set up at the Lutheran church in Kensett. The American Red Cross is also assisting.

At about 10 a.m., most downtown Northwood businesses appeared closed, with few cars parked on the streets. School buses could be seen traveling the streets carrying people, some of whom were wearing face masks. Northwood-Kensett schools were already closed in anticipation of blizzard conditions.

Some of the few people on the streets in downtown Northwood were Antwan Martin, his wife and six children, who were trying to figure out where to go.

Martin said a man knocked on the door of his apartment at the Schoolside Apartments and told him to evacuate.

“We just moved here from Chicago,” he said. “We’ve never been through anything like this.”

The Worth County Sheriff’s Office plans to release a news release later today after additional people are evacuated.

The National Weather Service issued a civil emergency message about the fire, calling it “a dangerous situation.”

The message stated residents who do not have transportation can be transported to Kensett from the Sheriff’s Office at 1000 Central Ave. If transportation to the Sheriff’s Office is needed, people should call 641-324-2481.

Short-term effects of sulfuric acid exposure include irritation of the eyes, nose and throat, teeth erosion and difficulty breathing. Long-term exposure may cause irritation of the skin and chronic inflammation of the nose, throat and bronchial tubes, according to the Centers for Disease Control and Prevention.

Northwood has a population of about 2,000 people, according to the 2010 U.S. Census.