Portland fire officials said the vacant Centennial Mills warehouse is expected to collapse overnight, or be carefully demolished if it remains standing after Sunday's blaze.
88 firefighters — about half of Portland Fire and Rescue's workforce — responded after flames were reported just before 4 p.m., but crews could not enter because of missing stairwells, holes in floors and unstable heavy-timber construction.
Firefighters attacked the blaze from the river and by air as flames were visible for miles; officials said no one was inside and no injuries were reported.
The 116-year-old Pearl District landmark had recently drawn police attention over squatting concerns and was slated for redevelopment to improve public access to the Willamette River.