Neighbor Jared Wilson said the 30-year-old woman was able to escape the two-bedroom ground-floor apartment and stood outside as heavy smoke and flames engulfed her home. All four children were 10 or younger, fire officials said.
"She couldn't speak she was just hysterically screaming," said Wilson, 27, who lives on the building's third floor.
A 32-year-old man in the same apartment also died, said police spokesman Officer Matt Peringer. The woman was taken to a hospital where she was reported in stable condition, said Fire Battalion Chief Ed Carolan.
The names of the victims and the relationship between the man and woman were not immediately available. No other injuries were reported and the residents of all 12 apartments in the three-story wooden building were evacuated and found temporary housing.
Peringer said a cause hadn't been found before investigators secured the scene for the night. They planned to resume their work Sunday morning, he said.
Chris Champoux and his wife were sleeping in their apartment in the building across a driveway from the units that burned.
"The heat actually woke my wife up," he said. "It was an inferno very horrific."
Crews from six fire departments responded, and investigators from the Bureau of Alcohol, Tobacco, Firearms and Explosives, the Washington State Patrol and a Seattle Fire Department canine arson detection unit were at the scene, though there were no immediate signs it was intentionally set, Peringer said.
Carolan said the fire was reported around 2:30 a.m. at the Sammamish Ridge Apartments and quickly burned the two units above it. All three were heavily damaged and the apartments next to them have smoke damage, he said.
Wilson said only about 30 seconds elapsed from the time he first heard shouting until his apartment was surrounded by heavy smoke and he was forced to flee. As he ran down the stairwell, he saw the woman, whose children he had often seen playing, screaming outside the building.
Wilson said he and another resident grabbed a fire extinguisher and the two tried to enter the smoke-filled apartment. "At that point, the whole place just went up" and they were forced away by the flames.
"It's tough thinking about the fact that she lost her whole family," Wilson said
The building is one of a complex of three-story buildings in a wooded area just northwest of downtown Redmond. It is about two miles north of the Microsoft Corp. campus and about 12 miles east of Seattle.
The buildings have smoke detectors but not sprinklers, which weren't required when the complex was built in the mid-1980s, Peringer said.
"It is an awful tragedy," said Teresa Lunsford, resident manager of the complex. She declined further comment.
According to Sammamish Ridge's website, it is managed by Pan Pacific Properties, a Seattle company that has nine apartment complexes in the Seattle area.