Six children were among eight people killed when a fire tore through a Chicago apartment building, described by officials as one of the worst blazes the city has seen in a long time.

“We have not had this in many, many, many years — this amount of fatalities and injuries in one location,” said the city's fire commissioner José Santiago, adding that two adults and a dog were killed in the fire.

A teenager and young adult have been taken to the hospital in critical condition for burns and smoke inhalation.

The fire was noticed first by a passerby who saw smoke at the rear of the building at around 4am on Sunday, according to the Chicago Fire Department. No fire detectors were found in the building.

“Our death count would have definitely been lower or non-existent if working smoke detectors were in this structure,” Chicago Fire Department spokesman Larry Langford said.

While officials said that the relationship between the deceased was unknown, one individual who later showed up at the scene said that the dead were his family — siblings, and cousins.

“By the time we got here, the whole house was on fire. They were taking out my cousins, my brothers,” Marcos Contreras, 15, told the Huffington Post website. “Just knowing that the fact I’m never gonna see them again. My brother, coming to my room, messing with me for no reason. It just — I don’t have words to explain the pain I’m feeling right now”.

Police officers race against time to save animals in a shelter from a wildfire

The cause of the fire is yet to be determined by officials, who have said that their preliminary investigation found that the fire started on the second floor — where the family was living — before engulfing the rest of the building. The first floor was not occupied.

Public records that the building had two code violations during its last inspection, in June. One of those violations indicated that an extension cord feeding power between two buildings was dangerous and hazardous.