(CNN) -- A fire at a house in Connecticut early Christmas morning killed two adults and three children, fire officials said.
Two other people made it out alive.
"It is a terrible, terrible day for the city of Stamford," said Mayor Michael Pavia, briefing reporters about the "horrible tragedy."
"There probably has not been a worse Christmas Day in the city of Stamford," he said.
Multiple calls came in shortly before 5 a.m., fire officials said.
The first firefighters on the scene attempted rescues within the home, but "were pushed back by intense flame and heat," said Acting Fire Chief Antonio Conte.
The cause remains under investigation. Due to the condition of the building, it will be days before investigators can determine what happened, Conte said.
Seven people lived in the house, Conte said. He had no immediate information on their identities or the conditions of the two who came out alive and were taken to the hospital.
The home is in Stamford's Shippan Point neighborhood, just in from the Long Island Sound, fire officials said.
CNN's Josh Levs contributed to this report.