Authorities say two children and their father were among five people who died on an Illinois highway after a truck carrying anhydrous ammonia overturned Friday night. 

The crash occurred around 9:30 p.m. on U.S. Highway 40, about a half-mile east of Teutopolis, according to the Illinois State Police (ISP). Multiple vehicles were involved and a truck hauling anhydrous ammonia began leaking after rolling over.

The semi-truck was carrying about 7,500 gallons of ammonia, of which 4,000 gallons leaked from the tanker, according to the ISP. As a result of the ammonia leak, about 500 residents near the scene were evacuated.

The Effingham County coroner said two of the fatalities were children under 12, according to NBC News. The ISP said multiple other injuries were reported. 

Responding agencies included the ISP, Illinois Environmental Protection Agency, Illinois Emergency Management Agency and Office of Homeland Security, Illinois Department of Transportation, Illinois Department of Public Health (IDPH), Effingham County Sheriff’s Office and Teutopolis Fire Protection District.

The EPA performed air monitoring within the community and evacuation zone and did not detect any levels of concern, the ISP said in a statement, and it “will ensure contamination resulting from the incident is properly addressed.”

The evacuation order has since been lifted, but residents have been asked to ventilate their homes. 

“IDPH is also working on guidance regarding testing of private water wells in the immediate vicinity of the incident to check for possible contamination,” the ISP said. “We remain in consultation with the local health department and the Illinois Department of Agriculture regarding animals and livestock in the area and procedures for transporting them for veterinary evaluation.”

The cause of the crash is under investigation by the ISP and the National Transportation Safety Board has sent a team to the scene.