A fire that turned explosive at a commercial structure in North Long Beach Friday afternoon appeared to be caused by an illegal THC extraction lab, a Long Beach Fire Department spokesman said Saturday.

Two people were hospitalized after being injured in the fire, which broke out shortly after 4 p.m. Friday in the 2200 block of 69th Street.

When fire units arrived at the business around 4:13 p.m. they witnessed fire coming from the roof of the structure, LBFD spokesman Jake Heflin said. Additional units were requested, turning the incident into a second-alarm fire. Los Angeles Fire County personnel were also called to assist with the incident, Heflin said.

As firefighters were attempting to contain the blaze, two compressed-gas cylinders inside the structure exploded, and heavy flames appeared to erupt from within.

Workers in neighboring buildings said the explosions “felt like an earthquake.”

The fire was eventually contained to only the affected building and put out, authorities said.

THC extraction labs are typically used to separate a crystallized concentrate from the marijuana flower to produce cannabis products. The method to extract the THC tends to use flammable chemicals such as ethanol and butane, which researchers have found to increase extraction efficiency and decrease extraction time from days to minutes.

The fire remains under investigation, according to authorities.

2 hospitalized in fire that turned explosive at North Long Beach business