(Reuters) - The U.S. National Transportation Safety Board (NTSB) will investigate a chemical spill in a small Illinois village north of Chicago on Thursday that sent 37 people to hospitals and forced nearby residents to shut their windows and shelter in place, authorities said.
Those sent to hospitals with "inhalation issues," none of which were life-threatening, included three law enforcement officers who were overcome after responding to a spill of anhydrous ammonia in Beach Park, Illinois, the Lake County Sheriff's Office said. Eleven firefighters were also hospitalized.
The NTSB is sending team of four to investigate the hazardous materials release. The team will begin on-scene work on Friday morning, the NTSB said.
The chemical leaked out of containers being pulled by a tractor in the municipality about 45 miles (72 km) north of Chicago, the sheriff's office said in a statement.
"This caused toxic plumes of the chemical to be released into the air," it said.
Because of the incident, which occurred at 4:25 a.m. local time, the sheriff's office urged all residents within a one-mile (1.6-km) radius to stay in their homes.
"Law enforcement and fire personnel are currently going door-to-door to check on residents to ensure they are safe in their homes and not in medical distress," it said.
(Reporting by Peter Szekely in New York and David Shepardson in Washington; editing by Jonathan Oatis and Bill Berkrot)