Two people were arrested early Thursday morning on suspicion of running a lab to extract THC from marijuana after an explosion blew off about half the roof a San Leandro warehouse and wounded two others allegedly involved in the operations, authorities said.

Officials responded around 4:40 a.m. to a report of an explosion at the commercial warehouse on the 1700 block of Timothy Drive near Highway 880 and transported two people with non-life-threatening injuries to a local hospital, said Lt. Ted Henderson, a San Leandro police spokesman.

One of the victims had a broken arm.

Two people were arrested on suspicion manufacturing hash oil illegally and authorities planned to arrest the other two taken to a hospital after they were treated, Henderson said. He added that authorities were still trying to determine if the lab had a license to operate.

Crews on scene for an explosion at a commercial building in San Leandro on the 1700 block of Timothy. Cause is under investigation. No injuries. Full update coming soon. pic.twitter.com/hdmOjdIXN5

— Alameda County Fire (@AlamedaCoFire) May 7, 2020

Henderson said he did not know exactly how the explosion occurred, but the process of extracting THC from the marijuana plant required butane, which caused the explosion. Fire officials said the blast sent debris approximately 2,000 feet down the block.

“Probably half of the roof is blown off,” Henderson said. “It was not small. … We have a few hours that we are going to be out here.”

Investigators were also trying to determine if the building was up to code and whether it had working fire alarms.