Fire swept through an apartment early Thursday, killing three young girls and critically injuring their mother, authorities said.

The woman and the girls, ages 1, 2 and 4, were unconscious and not breathing when firefighters arrived shortly before 5 a.m., Montgomery County fire department spokesman Pete Piringer said.

Firefighters found the youngest child on a bed, and the woman and two other children on the floor nearby, Piringer said. The children died a short time later and the woman was hospitalized in critical condition, he said.

Piringer said the fire is believed to have started in the kitchen, and was mostly confined to that area.