SAN BERNARDINO (AP) — Authorities say an explosion at a house near San Bernardino has left one person dead and two critically injured.

San Bernardino County fire officials say the blast happened in the neighboring town of Muscoy shortly before 7:30 p.m. Wednesday night, CBS2/KCAL9’s Stacey Butler reported.

READ MORE: NFL, LA County Go On Public Education Blitz To Block COVID From Super Bowl Festivities

Fire crews used heavy-duty equipment to retrieve the deceased’s body from the rubble.

The two critical patients were taken to a hospital.

The incident was initially reported as a possible gas explosion but San Bernardino County Fire has since learned the structure behind the house, built without a permit, was not connected to a natural gas line. They said gas was not a cause.

READ MORE: Cold Weather Alert Issued For Antelope Valley

“The Investigators’ preliminary investigation shows them that there was narcotic activity here at the residence and was likely a marijuana extraction lab,” said Cindy Bachman of the San Bernardino Sheriff’s Department.

“So they were making THC oil?” Butler said.

“Right. And in that process they used butane, and that’s probably what caused the explosion,” Bachman said.

MORE NEWS: Newsom, California Lawmakers Reach Deal To Bring Back COVID Sick Pay

(© Copyright 2014 The Associated Press. All Rights Reserved. This material may not be published, broadcast, rewritten or redistributed.)