Seattle Fire investigators have a lengthy investigation ahead as they work to determine the cause of a massive four-alarm fire in a lumberyard north of Seattle Pacific University on Saturday.

Firefighter responded to the 3500 block of Sixth Avenue West around 8:40 p.m. to tackle fires in structures owned by Gascoigne Lumber Company and Northwest Millwork. At the height of the blaze, three buildings and two large sheds were involved, according to the Seattle Fire Department. Two of the structures collapsed in the blaze, which could be seen as far away as Alki Beach.

Seattle City Light had to de-energize power due to the fire nearing a mainstream line. Seattle Fire reports multiple power lines caught fire during the blaze. Most customers had power back by Sunday morning.

Seattle Pacific University evacuated its residence halls during the fire, clearing all residents except for those in Hill Hall to return by 2 a.m. Sunday; they were moved to the Ashton Hall main lobby.

Gascoigne Lumber Company was established in 1926, and sells wholesale finish lumber and moulding supplier. Because most of what was in the structures was lumber, the fire spread more quickly, according to Seattle Fire.

Firefighters used hose lines and ladder pipes, with a fireboat called out to attack the fire from the waterfront on Saturday night. No occupants were believed to have been in the fully enflamed structures, according to Seattle Fire.

South and Eastside fire departments were dispatched to Seattle to provide support for other emergency calls while Seattle firefighters were involved with the lumberyard fire.

Crews remain on scene Sunday to ensure the fire is fully extinguished, at which point the investigation into the cause can begin.

Seattle Fire investigators determined a fire that destroyed the Seattle Elks Club #92 building near the Fremont Bridge last week was arson.