A gas pipeline explosion near Fresno, California on Friday injured at least 11 people and led to the closure of a major highway, authorities said, according to media reports.

The line was struck by a county equipment operator in a construction vehicle while building a dirt berm on the range, which is next to the high-traffic Highway 99, the Associated Press (AP) reported, citing officials. 

The number of injured persons is disputed in different news sources. Up to 15 people were injured in the incident, and four of them were critical, Reuters reported, citing officials.

The explosion hit a Pacific Gas & Electric (PG&E) Co. pipe carrying natural gas. The flames from the explosion reportedly reached over 100 feet into the air.

Traffic heading north along the highway was stopped by the explosion that took place at about 2:30 p.m., the California Highway Patrol said, the AP reported, adding that the highway was reopened three hours later.

A group of county jail inmates were reportedly doing cleanup work in the vicinity. Ten inmates and the operator were hospitalized for burn- and trauma-related injuries, of which three were said to be in critical condition, according to Fresno County Sheriff Margaret Mims, the agency reported. Three inmates had reportedly been evaluated and sent back to jail, and two deputies were being assessed for ringing ears and heat exposure.

Mims said her office would investigate whether the driver’s actions at the site had anything to do with the explosion. "Hopefully we'll be able to speak to the worker to see what action he was taking at the time," she said, according to the AP.

A spokesman for PG&E reportedly said the buried pipeline was damaged by a vehicle and that the flame was extinguished about an hour and a half after the blast. "Our thoughts and prayers are with those who are reported to be injured," another spokesman, Keith Stephens, said, the AP reported.

Earlier this month, California authorities brought a $1.6 billion penalty against PG&E for a 2010 blast that killed eight people in a San Francisco suburb.