Those within half a mile of the rail yard were told to leave the area.
A chemical leak from a railcar prompted officials to issue an evacuation order for residents in the Cleves and Whitewater Township areas in Hamilton County, Ohio, authorities said Tuesday.
Hamilton County's Emergency Management and Homeland Security Agency told anyone within half a mile of the rail yard to leave the area immediately.
Authorities confirmed the leak was styrene, a flammable liquid used to make plastics and rubber, according to the National Institute of Environmental Health Sciences.
"The risk of an explosion is our primary concern," an official said at a Tuesday night news conference. "We are asking residents within a three-quarter-mile radius to shelter in place as a precaution. Experts have assured us that this is well within the safety norms."
Officials said 210 homes were located in the designated evacuation zone, though how many people have been impacted was not immediately known. Those needing shelter were advised to go to the Whitewater Township Center, officials said.
Although authorities said at an 11 p.m. ET news conference that the leak had been contained, people were still urged to avoid the area.
"We feel we've made significant progress by separating the affected rail car from the rest of the train," an official said. "Monitoring and mitigation teams are working diligently to ensure everyone's safety. In the meantime, we urge residents to stay out of the area."
Authorities are closely monitoring air quality for styrene but said at the earlier news conference that they haven't yet determined the exact levels.
The train in question consisted of 29 cars, some of which were also carrying styrene, officials said.
"Our first priority upon arriving at the scene was removing anything in close proximity to the leak," an official confirmed.
Only one car was found to have leaked styrene, they said.
In response to questions on Tuesday night about when residents can return home, officials urged patience.
"We're not going to rush this. Once it's absolutely safe, we'll let everyone know. For now, we encourage residents to monitor social media and news outlets for updates," an official said.
In a post on Tuesday night X, Transportation Secretary Pete Buttigieg urged those in the area to follow the directions of officials.
Cleves Township is almost 17 miles from Cincinnati, Ohio, while Whitewater Township is about 22 miles away.