An arson investigation is underway after a fire at a Plaid Pantry convenience store in north Portland Tuesday night. The fire was reported just before 9 p.m. at the store on North Greeley Avenue near North Rosa Parks Way. Firefighters said they got most of the flames out in about 10 minutes. An employee working inside the store at the time told FOX 12 he didn’t see anything because he was in the back, but he heard a boom and came out front to find the inside of the store on fire. He said he tried fighting it with a fire extinguisher, but the flames were too big and he ran out. No injuries were reported.