The fire was reported at 6:45 a.m. at a home in north Oklahoma City, The Oklahoman reported.
Fire Battalion Chief Randy Cornelius said crews battled the blaze as firefighters found the bodies.
"This was an intense fire," Cornelius said. "It was pretty dangerous."
Fire Major Tammy McKinney confirmed the victims were four children and one adult. Another adult is in critical condition at a local hospital. Three of the family's pets also died in the fire.
Officials are investigating the incident.
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