In Weatherford, Oklahoma, a tanker truck incident led to the release of hazardous ammonia gas in a hotel parking lot, prompting the evacuation of hundreds of residents from the small city and resulting in dozens seeking medical attention, according to authorities on Thursday.

The situation unfolded as firefighters, equipped with gas masks, moved through Weatherford during the night, alerting residents to evacuate due to the anhydrous ammonia leak. By Thursday morning, the shelter-in-place order was lifted, restoring a sense of normalcy to the community.

Darin Farrell, president of Weatherford Regional Hospital, reported that the emergency room attended to 36 individuals affected by the leak. Of these, one patient was admitted in stable condition, while 10 others required transfer to hospitals in Oklahoma City. The condition of these transferred patients remains unknown.

Earlier, Police Chief Angelo Orefice noted that four individuals were in critical condition due to the exposure.

The tanker truck began leaking ammonia late on Wednesday night, leading to respiratory issues among those nearby, as explained by city officials during a press conference. This prompted a swift emergency response.

As a safety measure, between 500 to 600 people sought refuge in a shelter early Thursday, while others were instructed to stay indoors until further notice. Additionally, some nursing homes were evacuated, and local schools were closed for the day to ensure the safety of the community.

Trisha Doucet called police for help when she learned the leak was blocks away from where her mother was caring for her bed-bound 89-year-old grandmother. An ambulance was quickly dispatched to get her to safety.

Her grandmother, who is on hospice, was reluctant to leave. “But this is my house,” she said.

Doucet, who used to work as an EMT and knew the dangers of anhydrous ammonia, recalled telling her grandmother, “That’s the hardest part. I know it’s your house, but you really have to go.”

The driver of the truck carrying the gas had parked behind a Holiday Inn Express to get a room there for the evening, Orefice said. The cause seemed to be a mechanical failure on a valve or a faulty seal, the police chief said.

Anhydrous ammonia is used as a farm fertilizer to help corn and wheat grow. The colorless gas has a pungent, suffocating odor and can be deadly, especially at high concentrations, or cause breathing problems and burns to the skin and eyes.

Just last week, an anhydrous ammonia leak caused by an explosion at a plant near Yazoo City, Mississippi, prompted evacuations and sent a plume of yellowish smoke rising above the facility.

Two years ago, five people died in Illinois when a tanker truck spilled anhydrous ammonia after it was forced off a road by a passing minivan.

The cleanup in Weatherford – a city of 12,000 people about 70 miles west of Oklahoma City – could take several days, the police chief said.

“We pretty much got a lot of of this stuff diluted right now,” Orefice said, adding that authorities were working with environmental officials.

Authorities said the air quality was being monitored and that the tanker truck was no longer leaking. A number of agencies were assisting, including hazmat crews and an Oklahoma National Guard.

Industrial gas distributor Airgas said it was working with local authorities. “Anhydrous ammonia warrants cautious handling and management,” the Radnor, Pennsylvania-based company said in a statement, urging people in Weatherford to follow instructions from authorities in the area.

McCormack reported from Concord, New Hampshire, and Brumfield reported from Cockeysville, Maryland. Associated Press writers Heather Hollingsworth in Mission, Kansas, and John Seewer in Toledo, Ohio, contributed.