PORTLAND, Ore. (KOIN) — An arson investigation is underway after fire crews battled an early morning blaze Thursday at a vacant warehouse in Northeast Portland.

A fire investigator confirmed the fire was intentionally sparked by combustibles outside the building, sitting along Interstate 84.

Fire officials told KOIN 6 that a MAX train operator called the fire in around 3:30 a.m. Crews responded to the building off NE Multnomah Street near 25th Avenue, Portland Fire & Rescue tweeted.

Fire crews say they had difficulty accessing the building, forcing them to shut down the nearby railroad and MAX tracks.

Once inside, firefighters worked to put out the blaze which they said had been partly dampened by the sprinkler system.