CONCORD, N.C. (AP) — Firefighters were unable to save the lives of two children caught in an overnight house fire in North Carolina, which also left a third child hospitalized in critical condition, officials said Sunday.

No other occupants were found inside and the “parents were not home at the time.” The victims were not immediately identified and their ages were not disclosed.

Fire-fighting crews were dispatched to a one-story public housing duplex in Concord, northeast of Charlotte, shortly after 1:00 a.m. and found heavy fire coming from one of the units, the city said in a news release. Firefighters worked to extinguish the blaze and located three children inside.

They began life-saving efforts, but two of the children died at the scene, the news release said. The third was taken to a hospital in critical condition.

The occupants of the adjacent unit evacuated before firefighters arrived, according to the news release.

The cause of the fire is under investigation, the city said.