Five people died after a crash involving multiple vehicles including a tanker carrying anhydrous ammonia that overturned in Illinois on Friday night, leading to a leak of the toxic gas and prompting residents within a one-mile radius of the crash site to evacuate, officials said.

The truck rolled over on U.S. Highway 40, about half a mile east of Teutopolis, Ill., which is about 90 miles southeast of Springfield, around 9:25 p.m. on Friday, releasing a large plume of anhydrous ammonia and causing dangerous air conditions, officials said at a news conference on Saturday morning.

Kim Rhodes, the Effingham County coroner, said five people had died as a result of the crash, adding that it was possible additional fatalities could be reported later. It was not immediately clear how the victims died.

Three of the victims were from the area, including a child and an adult who were from the same family, Ms. Rhodes said. Two other victims were from Ohio and Missouri, she said.

Chief Tim McMahon of the Teutopolis Fire Protection District said that five people with injuries were airlifted to hospitals and another victim was taken to a hospital in a vehicle. Their conditions were not immediately known.

It was also unclear how many people had been evacuated. About 1,500 people live in the village of Teutopolis.

Because of the dangerous plume of gas, emergency crews had to wait before responding to the crash, said Sheriff Paul Kuhns of Effingham County, which includes Teutopolis.

“They had to mitigate the conditions before they could really get to work on it, and it was a fairly large area,” he said.

The National Transportation Safety Board was sending a team to help with the investigation. Traffic had been rerouted to Highway 40 earlier on Friday because of a separate crash nearby.

Chief McMahon said at the news conference that a hazmat team had patched the ruptured part of the tanker, which slowed but did not stop the leak.

Anhydrous ammonia — often used in manufacturing, refrigeration and agriculture — is a toxic gas that can be corrosive to human tissue upon contact, according to the Centers for Disease Control and Prevention.

“It’s terrible,” Sheriff Kuhns said. “It’s bad stuff if you are involved in it — breathe it especially — because it gets in your airways, in your lungs.”

Chief McMahon said that the direction of the wind had changed three or four times overnight, further complicating the response to the crash. Crews were set up in multiple locations to respond to the gas leak based on the wind changes, he said.

The National Weather Service was providing officials with forecast updates, Sheriff Kuhns said. “Any amount of wind or weather will complicate this process immensely,” he said.

Crews were still at the crash scene early on Saturday morning. It was unclear when evacuation orders would be lifted.

“Once we get the product offloaded and away from the scene, I think things will return back to normal fairly quickly, but this is a complicated situation,” Sheriff Kuhns said. “I understand how frustrating that would be to not be allowed to travel or to go back home, but we really need to focus our resources on this spill.”

Illinois State Senators Steve McClure, Jason Plummer and Chapin Rose said in a statement that they were monitoring the situation.

“Our hearts are with the families of those who passed in this awful tragedy, and with the emergency personnel who have risked their own safety to help others,” they said. “Please stay clear of the area and allow first responders to work.”