A fire broke out in an abandoned home in Fresno, Calif. on Sunday killing five people, and critically injuring another after they became trapped by the flames, authorities report. The fire was first reported at 6:44 a.m. by a neighbor, who saw the flames and heard people screaming and pounding against a window for help, according to The Fresno Bee.

Responding fire crews arrived to see the building engulfed and found the six victims trapped inside one bedroom, where they had apparently tried to a smash a window open to escape the fire and smoke. They apparently got into the building through a pried window, however the fire was most intense there, preventing them from using it to escape.

Four of the victims died at the scene, while the fifth died at the hospital, reported ABC News. Three of them were identified as Irene Hinojos, 36, Monique Amaral, 28, and Anthony Zavala, 37. The names of the others were withheld until the families could be contacted.

The lone survivor, who remains unidentified, was admitted to Community Regional Medical Center where he/she remains in critical condition.

Fresno fire spokesperson Pete Martinez noted that while its unknown what killed the victims, factors indicate that they died from smoke inhalation, according to the Associated Press.

In the meantime, investigators are looking for witnesses and video footage to determine the cause of the fire.