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'It sounded like a bomb went off': Backdraft explosion rips through New Jersey building

A backdraft caused a surprise explosion during a six-alarm fire in Harrison, New Jersey that injured five firefighters, but all are expected to survive.

Five firefighters were hurt when the backdraft from a six-alarm blaze set off a massive explosion at a New Jersey building Sunday afternoon, authorities said.

The injuries were not considered life-threatening, but one firefighter was severely cut by flying shards of glass after the explosion shattered a window at the Harrison, N.J., building, fire officials said.

"It sounded like a bomb went off, to be completely honest," said Captain Robert Gillen of the Harrison Fire Department.

Dramatic video footage recorded by a witness shows a monster fireball ripping through the two-story structure, masking adjoining buildings in a thick cloud of smoke.

"There was heavy, black smoke. Debris was thrown from the building. A couple firefighters were literally thrown out of the building because the explosion was so powerful," Gillen said.

An unidentified man is heard in the video instructing people to turn away from the smoke spewing out of the building.

"Get down! Get down! Get down! Shield your eyes," the man can be heard shouting.

The original blaze broke out Sunday morning and raged for hours before firefighters stamped it out. Gillen said officials do not yet know what triggered the fire, but it reportedly began in the kitchen of a Mexican restaurant on the building's ground floor before spreading to an adjoining apartment complex.

Authorities said at least five families living in adjacent buildings were displaced by the blaze but suffered no injuries. Some of the private residences damaged by the fire will need to be razed, Gillen said.

A spokesperson for the New Jersey Red Cross told NBC New York that the organization was assisting 17 people forced to leave their homes.

All the injured firefighters were transported to a local medical center and released, according to Gillen.