Two people with significant injuries were taken to Harborview Medical Center in Seattle, Bellevue Fire Department Lt. Rich Burke said.
The hospital received two men. One was in serious condition in intensive care and the other was in satisfactory condition, spokeswoman Susan Gregg said.
Five people with minor injuries were taken to hospitals on Seattle's east side. They include a firefighter who cut her hand, Burke said.
There were multiple 911 calls when the fire broke out at about 6:30 a.m. at the Hampton Greens, a complex with about three dozen buildings on 16 acres.
There were initial reports of an explosion, Burke said. It took about an hour-and-a-half to control the fire, and there were about 80 firefighters from Bellevue, Redmond and Kirkland at the scene, along with about 20 police officers, he said.
The fire nearly destroyed one three-story building with 10 units, Burke said. Firefighters would have to remove a heavy tile roof before investigators could go inside. It may take days for police and fire investigators to determine the cause, he said.
Displaced residents were sheltered in a bus and are receiving aid from the Red Cross.
One resident of a neighboring building, Caleb Petrie, told KOMO Newsradio that he awoke to an explosion that shook the complex. When he looked out, he saw flames shooting from both sides of the building. He saw one man run out with his clothes on fire.
Petrie ran outside and helped one woman who jumped from her third-floor apartment, breaking at least one leg. She told him her cats were already dead when she jumped.
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