Four children are dead and six of their relatives in hospital after someone tried to wash away a pesticide sprayed under their Texas home, unleashing a poisonous gas.
Amarillo fire officials said phosphine gas was likely emitted when water was mixed with the pest control chemical used to kill mice.
Siblings Felipe Balderas, seven; Johnnie Balderas, nine; Josue Balderas, 11 and Yasmeen Balderas, 17, all died, WJLA reported.
One child died at the scene and three others died at a hospital. The childrens' six relatives are "not out of the woods yet," fire officials said.
Crews who responded to a call to the home at 5am Monday (12pm Monday NZDT) originally thought it was related to carbon monoxide poisoning, Amarillo fire Captain Larry Davis said in a statement.
Davis told the Amarillo Globe-News he wasn't sure how long the residents had been exposed to the phosphine gas before a visitor arrived on Monday and found everyone sick 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.
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.
A GoFundMe page has been set up for the family following the tragic incident.
"The Balderas family is heartbroken today. They have lost four members of their family," Terry Rodriguez, the teacher of one of the deceased, wrote on the page.