Gas line explosion closes Highway 99 in Fresno, Calif., injures at least 11 (VIDEO)

FRESNO, Calif. (AP) — Fresno County Sheriff Margaret Mims says 11 people were injured in a large gas-pipeline explosion that shut down a major highway in the region.

Mims says three of the people injured are in critical condition and one is in serious condition. They are at a burn and trauma center in Fresno.

Officials initially said 15 people had been injured.

It was not clear what caused the explosion at the Fresno County Sheriff's gun range that brought traffic in the area to a halt.

But authorities say it occurred while a county equipment operator was working with a jail inmate crew to expand a road on the range alongside heavily traveled Highway 99.