GRANBURY (CBSDFW.COM) –  Six people are dead after a structural fire broke out at a doublewide mobile home in Granbury Sunday, Hood County Fire Marshal Brian Fine said.

Fire officials responded to the fire in the 4500 block of Wildwood Circle just after 6 a.m. Three victims were burned and treated at Parkland and JPS hospitals. Fine said three men and three women between 18 and 30 years old died inside the mobile home. Fire officials did not identify the victims.

Officials are unsure how the fire started, but the “cause does not appear suspicious,” Fine said.

“We got on scene and found a structure that was fully involved, flames shooting out the windows,” Fine said. “We’re still trying to identify the six victims as soon as we can.”

Fine said the doublewide was a “weekend home” and there was a birthday party there Friday night for one of the victims. There were reportedly nine people at the home at the time of the fire. They went to bed just after 2:30 a.m., Fine said.

“This is the worst fire I have been on in terms of fatalities,” he added.

One of the teenage victims who escaped the fire said she woke up and tried to get those inside out. When she couldn’t, Fine said she ran to a neighbor’s house to call police. The fire took more than two hours to put out.

“By then, we knew none of the victims would still be alive from the fire so we tried to suppress the fire,” Fine said.

A neighbor said the home belongs to Kurt Reineck, who is a father of an 18-year-old son and a 16-year-old daughter. Reineck is in San Antonio on business and knew about the party.

Reineck’s daughter was involved in an accident before the fire. She was taken to a nearby hospital with serious injuries. When Reineck called neighbor Tom Tanner to check on his son, he found more bad news.

“He asked me if the red Firebird was in the driveway and the reason he was asking that was because it was his son’s,” Tanner said. “They are trying to reach (the son) but they haven’t reached him.”

Authorities said none of the victims were Hood County residents, which is why identifying those involved was difficult.