PORTLAND, Ore. --
Four semi-trucks were destroyed in a fire early Wednesday morning at a Swan Island freight yard, fire officials said.
A Freightliner worker spotted one of the burning rigs, fire crews said, and called 911 at about 3:15 a.m.
When firefighters arrived, they found the trucks in flames. Fire officials said four 50-foot trailers were also burned and severely damaged.
Fire investigators said mechanical or electrical malfunction caused the fire.
Damage is estimated at $1 million.
The freight yard, located on the 5300 block of North Channel Avenue, is surrounded by a fence and the entrance was locked, investigators said. Firefighters had to cut through the fence to battle the blaze.
The lot is used for overflow and Freightliner stores new, experimental rigs there.
Christina Hart said she witnessed the fire and heard explosions.
"I ran over here and it was in flames -- huge flames. There were four trucks on fire," Hart said. "There were a couple of good explosions, probably tires or fuel tanks."
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