All 32 of the people who live in the complex were able to escape without injury, said Kyle Moore of the Seattle Fire Department.
Crews responded to the scene, at 1100 S. Massachusetts St., at about 5:35 a.m. after receiving 911 calls from residents.
When firefighters arrived, flames had extended to three units of the building and a second alarm was sent out as residents were evacuated.
Crew quickly brought the blaze under control. No occupants were found in the burned units. The fire was completely extinguished by 6:30 a.m.
One resident, Stephanie Bielekova, told KOMO News that the fire began with an explosion in the unit next to hers.
"I was asleep and I just heard a big bang, which woke me up, and I ran to the kitchen and all of the items had fallen off my shelf and I heard screaming from next door," she said.
"And I ran out to the balcony and I saw just smoke coming out of the window. And then our neighbor, I could hear him yelling, 'Fire! Fire!' And I just grabbed what I could and ran out."
Bielekova says the neighbor in the apartment next to hers later told her he awoke and saw flames spewing from the area around his oven.
Investigators later said the cause of the fire was accidental. A refrigerator ignited butane gas, causing an explosion.
Damage was estimated at $300,000.