Memphis, TN — A natural gas leak caused an explosion that injured seven people in a home in Memphis, Tennessee, fire officials said Friday.

Four adults and three children were taken to hospitals with second- and third-degree burns on 70% to 80% of their bodies after the explosion Thursday night, Memphis Fire Department Lt. Wayne Cooke said in a news release.

The adults injured in the explosion are in their 30s. Cooke said the children are 4, 10 and 13 years old.

When firefighters arrived, they found that the exterior of the one-story, wood-frame house had collapsed. They searched the house but found that everyone had already exited, Cooke said.

The home did not have a working smoke alarm, Cooke said. Fire investigators determined the cause as a natural gas leak from a water heater inside the house, Cooke said.

The explosion caused more than $15,000 in damage to the house and its contents, Cooke said.