A fire destroyed a building that was under construction in Oakland on Thursday night.

The fire, at 919 Stanford Ave., shot flames high into the sky. Firefighters put the fire out within an hour.

Lana Que, who lives behind the burned two-story building, said the fire started around 9:30 p.m. She was sitting on her couch when she saw flames.

“I thought my backyard was on fire,” she said, watching the building burn while standing barefoot with her year-old daughter in her arms. She ran out of her house without putting on her shoes. “I know better than to not take fires seriously.”

She said the building was a former printers’ office, in the process of being converted to seven to nine loft-style apartments.

Fire investigators with Oakland Fire Department were on the scene Thursday night and interviewing witnesses. Dozens of onlookers watched as the building burned and as firefighters worked to contain the blaze.

A witness at the scene told The Chronicle the structure had been under construction for a couple years.

Now Playing:

The cause of the fire is unknown.

Erin Allday is a San Francisco Chronicle staff writer. Email: eallday@sfchronicle.com Twitter: @erinallday