Witnesses said one woman's leg was badly broken when she jumped from a third-story window to escape the flames. Another man was seen on fire as he ran from the burning three-story building.
It all started with an explosion at about 6:20 a.m. that some residents likened to a bomb or an earthquake.
Firefighters quickly responded to the blaze, at the Hampton Green Apartments at 4747 148th Ave. NE in Bellevue. When they arrived, smoke and flames were already belching from one unit at the complex.
The blaze quickly spread from that unit to several others, and a second alarm was called out as crews scrambled to combat the now-raging fire.
By the time the fire was extinguished, hours later, it had destroyed one three-story building with 10 units and more than 100 firefighters and police officers were on the scene, said Fire Department Lt. Rich Burke.
Caleb Petrie, who lives in the neighboring apartment building, told KOMO Newsradio he awoke to a huge explosion that shook the complex. When he looked outside he saw flames shooting from both sides of the building - and watched in horror as one man ran out with his clothes on fire.
Another witness, David Lee, said, "I heard a large blast ... it sounded more like a loud something falling on the roof. ... And I came outside and I heard people screaming."
Lukas Anderdejewaki, who lives in one of the units destroyed by the blaze, escaped with his life and his wedding photo.
"I ran out, I grabbed my picture and a jacket ... then I saw how serious it was," he says, adding that the flames were too hot and intense to grab anything else.
But when he heard a neighbor scream from an apartment on the upper floor, he ran back toward the flames.
"I heard somebody on the opposite side yelling. I tried to get to the door, and that's how I burned my hand," he says. "It was already just melting and too hot." He then was overcome by smoke.
Meanwhile, other neighbors out on the lawn saw the woman screaming from her burning upper-floor apartment as flames roared behind her. They coaxed her to her balcony and yelled at her to jump, says neighbor Bai Drammeh.
Seconds later she did jump, badly breaking at least one of her legs when she hit the ground.
Petrie says he ran to the woman's aid when she landed on the grass. He said she seemed more devastated about her pet cats than about her injuries.
"She said that by the time she jumped out, she had cats, and the cats were already dead by the time she jumped out. So the shock wave, whatever exploded, must have taken out the cats - it's kind of sad," Petrie said.
Meanwhile, neighbors who live in undamaged buildings at the complex began taking the victims into their homes.
"When the initial units arrived, people were already taking (the victims) into the homes, wrapping them in blankets - just a great community working together," said one fire official.
Two male patients were taken to Harborview Medical Center. One was later listed in serious condition and the other in satisfactory condition.
Five other patients with less severe injuries were taken to other hospitals on the east side, according to the Bellevue Fire District. One firefighter sustained lacerations to her hands.
The cause of the fire was not immediately known, but officials said the building was not equipped with natural gas, so that possibility has been ruled out.
The federal Bureau of Alcohol, Tobacco, Firearms and Explosives was called in to help investigate the fire and determine whether it was sparked by illegal activity.
A King County Metro bus later responded to the scene to provide temporary shelter to people burned out of their homes. Red Cross officials also were helping victims to find temporary housing.