The blaze was being investigated as an arson, Vancouver police spokeswoman Kim Kapp said.
The Oregonian and The Columbian newspapers reported that public records show that Tuan and Lori Dao and their six children had lived in the house in a middle-income subdivision of one-story homes.
Officials haven't yet identified the victims. Autopsy findings were not expected to be available until Tuesday or Wednesday.
One neighbor, Kathy Larsen, said the family had moved out of the house but the father had recently moved back in. The Oregonian quoted another neighbor, Carol Kumanchik, as saying she had seen the father and his sons riding bikes on the street last Friday.
Jon Himes and Courtney Claybin, who live in a house just down the block, said their surveillance camera showed the father's car going past their house at 12:30 a.m. Sunday, apparently on the way to his house.
There was an explosion about an hour later that shook the neighborhood and the house caught fire. The flames were brought under control around 2 a.m.
Firefighters entered the home, moving aside debris, Kapp said. Initial reports said two people died in the fire, but more bodies were found.
"As they (firefighters) were able to access more and more parts of the structure, they were unfortunately able to locate more bodies," Kapp said. "It is very time-consuming to go through debris that is also evidence."
Investigators with the federal Bureau of Alcohol, Tobacco, Firearms and Explosives were at the scene Monday along with local investigators.
The Oregonian reported that Tuan and Lori Dao have four sons, ages 6, 11 and twin 9-year-olds, and two daughters, ages 7 and 12.
The Columbian reported that according to court documents, the Daos filed for bankruptcy last year with $158,000 in credit card debt and $2,000 in gambling losses. They owed $262,000 on the home that burned, which was valued at $179,000, the newspaper reported.
