LINDEN - Authorities say carbon monoxide poisoning likely caused the death of a 9-year-old boy and seriously injured his 10-year-old sister at their family's home in Linden.

Police responded to the Passaic Avenue home around 7:25 a.m. Tuesday. The children's 45-year-old mother called 911 after she had found them unresponsive in their bedroom.

The mother tried administering CPR on the boy, but he couldn't be revived.

According to the Linden Fire Department, there were high levels of carbon monoxide found throughout the home.

Linden police spokesman Capt. James Sarnicki says that the batteries inside the family's carbon monoxide detector were either old or corroded and it wasn't functioning.

“This incident highlights once again why carbon monoxide is called the silent killer, because it’s odorless,” Sarnicki says.

The boy was pronounced dead at a hospital a short time later. His sister is hospitalized in "extremely critical condition."

Officials say it appears the carbon monoxide levels may have been caused by the improper venting of fumes from the home’s steam boiler located in the basement. This is directly under the children’s bedrooms.

The investigation is ongoing.

The Associated Press wire services contributed to this report.