A leak in a tractor-trailer carrying anhydrous ammonia caused a chemical spill in Illinois on Thursday.
CNN  — 

A leak in a container holding hazardous chemicals created a massive chemical spill early Thursday and sent 37 people to the hospital, including seven in critical condition, said authorities in Beach Park, Illinois.

One of the patients in critical condition is a firefighter.

A preliminary investigation found that the containers, which held anhydrous ammonia, were being towed by a tractor on Green Bay Road in Beach Park, a village north of Chicago, Sgt. Christopher Covelli of the Lake County Sheriff’s Office said.

Anhydrous ammonia, a colorless gas with pungent fumes, can cause unconsciousness and even death when inhaled. The chemical is commonly used by farmers as an agricultural fertilizer, according to the Centers for Disease Control and Prevention.

The spill created a plume of chemical smoke, Covelli said.

Those transported to hospitals had inhalation issues, the Lake County Sheriff’s Office said on its Twitter account. While some have been released, seven were in critical condition, including a firefighter, Covelli told CNN.

A sheriff’s sergeant, deputy, a Zion Police officer and 11 firefighters who responded to the scene and breathed in the fumes are among those in the hospital, the Lake County Sheriff’s Office said.

The leak has since been contained, said Mike Gallo of the Lake Forest Fire Department. Officials are monitoring the plume and advised anyone within a one-mile radius of the spill to stay inside with their windows closed and keep air conditioning and heaters off.

In a statement, Sheriff John Idleburg praised the police and fire officials who responded.

“I wish to take a brief moment and commend all of our Lake County Sheriff’s Deputies, police officers from nearly twenty area police departments, and all of the firefighters who risked their lives today to help others. You are an amazing group of men and women,” Idleburg said.

“To those who remain in the hospital, the men and women of the Lake County Sheriff’s Office wish you a fast recovery.”

The spill caused several schools in Beach Park to close for the day, police said.

CNN’s Melissa Alonso contributed to this report.