A semitruck carrying 7,500 gallons of anhydrous ammonia overturned in Illinois in a multi-vehicle crash that caused five fatalities and sent another five people to local hospitals, officials said on Saturday.

The accident, which involved "multiple" vehicles, happened about a half-mile east of Teutopolis, Illinois, on U.S. Highway 40 Friday at about 9:25 p.m. local time, authorities said in a statement reviewed by CBS News. The impact of the accident caused the truck to begin leaking. That prompted the evacuation of 500 people, according to a news release from the Illinois Environmental Protection Agency.

According to early estimates, about 4,000 gallons have been released, and the leak has been "partially patched," the news release said.

Effingham County Coroner Kim Rhodes said five people died and five were flown to hospitals with unknown conditions.

An official from the Illinois State Police called the accident "very serious" and described the situation as "fluid" during a news conference held on Saturday morning. 

Effingham County Sheriff Paul Kuhns told reporters that there was a "large plume" from the ammonia leak. Because the leak caused "terribly dangerous air conditions in the northeast area of Teutopolis," an evacuation was ordered within an approximate one-mile radius of the crash, Kuhns said. Evacuation orders for some areas were lifted Saturday evening, Effingham County reported. 

Officials declined to comment on what caused the deaths. 

The air conditions meant emergency responders had to "wait" and "mitigate the conditions" before they could "get actual access" to the crash site, Kuhns said. Kuhns said the crash site covered a "fairly large area." The highway between Teutopolis and Montrose is closed. 

"We have a lot of brave firemen, EMT, hazmat specialists, police officers that are working on the scene as we speak," said Kuhns.  

The National Transportation Safety Board said in a statement shared Saturday on X, the social media site formerly known as Twitter, that it will investigate the crash in coordination with the Illinois State Police and the Effingham County Sheriff's Department. 

Inhalation of anhydrous ammonia, which is toxic, can be fatal at high concentrations. The ammonia can also burn the skin and eyes, and cause severe respiratory injuries.  In the news conference, one official called the substance "terrible." 

Teutopolis is a town of just over 1,600 people about 92 miles southeast of Springfield, Illinois, the state's capital. 

The Associated Press contributed reporting.

In:
• Illinois
• Deadly Crash

Kerry Breen

Kerry Breen is a news editor and reporter for CBS News. Her reporting focuses on current events, breaking news and substance use.