Five people are dead and five more seriously injured after a tanker truck overturned in a multivehicle accident in central Illinois on Friday evening, spewing hazardous chemicals and prompting evacuations, authorities said. Multiple crews continued to try to contain the chemical leak on Saturday.

Effingham County Coroner Kim Rhodes said the five dead included three members of a family — an adult and two children under 12. Rhodes didn't say where the family was from. The other two killed were adult motorists from out of state, Rhodes said. In addition, five people were airlifted to area hospitals; their conditions were unknown.

Emergency responders were on the scene Saturday morning, and road closures blocked residents from reaching their homes. Representatives from the U.S. Environmental Protection Agency were also at the site of the spill Saturday. The semi-truck was carrying about 7,500 gallons of anhydrous ammonia and more than half of the toxic chemical compound had leaked out by Saturday, the Illinois Environmental Protection Agency said in a press release. The leak has been partially patched, the agency said.

Federal regulators are investigating the cause of the crash, the National Transportation Safety Board said Saturday.

Tim McMahon, chief of the Teutopolis Fire Protection District, said the tanker began leaking after it rolled over into a ditch.

The crash happened about a half mile east of Teutopolis in the central part of the state.

The crash caused a plume of anhydrous ammonia to escape, and residents within a 1-mile radius, including northeastern Teutopolis, were told to evacuate. The highway was also closed, police said.

"The public should avoid the area," Illinois State Police said in a press release.

About 500 people have been told to evacuate, and evacuation orders were expected to remain in place through Sunday morning if not longer, authorities said.

The crash happened on Highway 40 after another accident in the region caused traffic to be rerouted, police said.

"Crews are working to contain the leak while first responders and emergency workers continue to respond to the incident," police said in the release.

Teutopolis has a population of about 1,600.

What is anhydrous ammonia?

Anhydrous ammonia is a gas that's commonly used in the agriculture industry and sometimes in refrigeration.

It is stored as a liquid under pressure and becomes a toxic gas when released, according to the Mississippi State Department of Health.

The compound can be a health hazard if safe handling procedures are not followed. Effects of inhaling anhydrous ammonia range from lung irritation to severe respiratory injuries, with possible death if a person is exposed to higher concentrations. Anhydrous ammonia is also corrosive and can burn the skin and eyes.

"It's terrible, it's bad stuff if you are involved with it and breathe it, especially," Effingham County Sheriff Paul Kuhns, who oversees law enforcement for Teutopolis, said at a Saturday press conference.

If people come in contact with it, the CDC recommends immediately removing them from the source and calling a poison control center or seeking medical care.

In 2019, dozens of people were sickened in suburban Chicago after the valves were left open on tanks of anhydrous ammonia en route from a farm in Wisconsin to another farm in Illinois, creating a toxic gas cloud. Seven people were initially hospitalized in critical condition in that event. A tank leaking anhydrous ammonia pulled by a tractor released a plume over the northern Chicago suburb of Beach Park.

And in 2002, a train derailment released anhydrous ammonia in Minot, North Dakota, killing one man and injuring hundreds of others, causing burns and breathing problems.

Motorists in 'tight-knit community' told to turn around

Phillip Hartke, 75, who lives in Teutopolis but farms with his son outside of town, said he finished harvesting corn at about 9:30 p.m. on Friday. Driving home, as he neared the center of town, he could smell anhydrous ammonia. When he reached US 40, emergency vehicles swarmed the area.

“Firefighters advised us right there: ‘Evacuate to the west,'” Hartke said.

Hartke estimated that 85% of Teutopolis was subject to the evacuation. He and his wife are staying with his son. Such familial ties should serve most evacuees well.

“'T-Town' is a tight-knit community,” Hartke said. “Many people have sons and daughters, aunts and uncles within 5 or 6 miles of town.”

The Teutopolis Civic Club had scheduled its third annual Oktoberfest on Saturday at the village banquet hall, serving $3 German bratwursts and $3 pork burgers, among other options.

But on Saturday, organizers wrote on Facebook that they canceled the event in the wake of the fatal accident. Instead, into the evening, they served bratwursts, hot dogs and burgers at a local business, located south of the evacuation area, for free to anyone hungry and to first responders.

Contributing: Associated Press; Eduardo Cuevas, USA TODAY