Four children have died and six people are in hospital after a poisonous gas was released when someone tried to wash away a pesticide sprayed under a home, according to officials in Texas.
Phosphine gas was likely released when water mixed with the pest control chemical, Amarillo fire officials said.
A specific cause of death had not been released for the four children on Monday afternoon.
The other six people who were in the home are "not out of the woods yet", fire officials said.
Crews who responded to a 5am call to the home originally thought it was related to carbon monoxide poisoning, Amarillo fire Captain Larry Davis said in a statement.
One child died at the scene and three others died at a hospital.
Officials did not release any identifying information, including the children's ages or whether they were related. Mr Davis said all four people who died were residents of the home.
Mr Davis told the Amarillo Globe-News he was not sure how long the residents had been exposed to the phosphine gas before a visitor arrived on Monday and found everyone ill before calling 911.
Phosphine gas can cause respiratory failure and in severe cases can cause a pulmonary edema, which fills the lungs full of fluid, he said.
Mr Davis said about 10 first responders from the police, fire and medical response departments were also taken to the hospital as a precautionary measure, but none had shown symptoms of illness.