There was a tragic start to Thanksgiving in Thornwood after a house fire has left one person dead.

Fire officials say the flames broke out at a home at the corner of Kensico Road and Warren Avenue around 5 a.m.

When firefighters got there, flames weren't visible on the outside right away.

Chief James Gedris says the four people inside didn't even know there was a fire.

Firefighters had to knock on the door to get them out.

Gedris says flames grew quickly from the basement and started to extend to the upper floors.

It took seven fire departments about an hour to put it out.

One of the four residents did not make it out alive. A family friend tells News 12 that the man who died was 26 years old. 

Officials are still investigating the exact cause of the fire, but they say it appears to be an accident involving electricity.