PORTLAND -- Investigators were still trying to find the cause of the five-alarm fire that destroyed the Thunderbird On The River, on the west side of the Interstate 5 bridge in Jantzen Beach early Sunday morning.

Firefighters said the damage estimate was at $5 million. Officials from the federal bureau of Alcohol Tobacco and Firearms were in charge of the investigation. Arson had not been ruled out but a cause would likely take days to discover, investigators said.

The blaze broke out shortly before 3 a.m.Sunday as crews arrived to find flames shooting through the roof of the western side of the complex at 1401 N Hayden Island Drive. Firefighters called the incident to five alarms at around 4 a.m. with more than 200 crew members working to control the blaze.

Your Pics: Jantzen Beach hotel fire

Three of the six units were a total loss and a fourth unit is still burning. The complex consists of six buildings connected by hallways. Five of the buildings were burned. It was expected to smolder for several days.

They ll have to do a lot of digging to get to the seat of the fire, Fire Inspector Ron Rouse said. They ll also have some dogs that come in and they can kind of sniff for accelerants.

The last time Portland firefighters battled a five-alarm fire was in 1999, a spokesperson said.

Twenty fire engines, 5 trucks and three fire boats battled the blaze with seven Chief Officers and a mobile command unit coordinating crew members.

History: Thunderbird hotel

Photos: Local photographer's HDR images of hotel before blaze

The hotel has been vacant since 2005.

There were no reports of any injuries, but emergency crews are making efforts to keep people out of the buildings.

The freeway was affected for a few hours overnight because of its proximity to the fire. The hotel on the east side was not affected, authorities said.

KGWReporters MarkHanrahan and Tim Gordon contributed to this report

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