REDDING, Calif. -

Firefighters battled a large structure fire in east Redding Sunday morning.

Every available unit from the Redding Fire Department responded to 3100 block of Lawrence Road around 9:30 a.m. after receiving reports of an explosion in an apartment complex.

Multiple apartment units were burning as firefighters rushed to contain the blaze. Flames could be seen raging through the roof of the single-story building. One person was injured in the fire sustaining significant burns.

Battalion Chief Cullen Kreider, the incident commander, would eventually call a third alarm on the fire, meaning the city called in off-duty personnel, and asked for help from agencies outside the city. CAL FIRE / Shasta County Fire, Bella Vista, and Anderson were among the agencies who helped.

The fire was extinguished around 11:30 a.m. All told, 10 units were rendered uninhabitable by the fire. Four of those units were considered destroyed. The Red Cross is assisting displaced residents.

On Sunday afternoon, deputy fire chief Gerry Gray with the Redding Fire Department said the cause of the explosion and fire was the production of hash oil.

Hash oil or honey oil is a concentrate extracted from marijuana usually made using butane.

Redding Police identified the injured person as 27-year-old Christopher Hightower.

Police said Hightower was by himself inside of an apartment operating a marijuana honey oil extraction lab.

Hightower was transported to Mercy Medical Center for his injuries.

He was later flown out of the county to a burn center to be treated for his injuries and is in critical condition.