Four children died after someone at their home sprayed water on a previously applied pesticide, causing a reaction that produced toxic phosphine gas, officials in Amarillo, Texas, said.
At least five other people were hospitalized in Monday's incident.
Fire Capt. Larry Davis said a family member had used water in an attempt to wash away the pesticide -- aluminum phosphide -- which had been applied under the home.
The incident preliminarily has been ruled an accidental poisoning, Davis said.
There were 10 people inside the mobile home at the time, according to Davis. Crews arrived at the scene just after 5 a.m. after receiving a call that something was wrong and that people at the address were sick.