DENVER (KDVR) -- Two people were injured and three families were displaced after an early Thursday morning fire in Northglenn in which first responders heard explosions as they arrived, according to North Metro Fire Rescue.

Multiple calls came in from the Huntington Square Apartments near 105th Place and Washington Street about an explosion between 4 a.m. and 4:45 a.m., North Metro Fire Rescue officials told FOX31's Lisa D'Souza. In an update posted on X, North Metro Fire Rescue said arriving crews saw heavy smoke and heard more explosions coming from the building.

Residents told D'Souza they heard explosions and some neighbors jumped in to try and extinguish the blaze before the fire crews arrived.

"The person that lives there had came outside, and (a neighbor) went in and he extinguished it," one resident said of the fire. "I think he saved us honestly because right after that there was another little explosion noise, and then it was just a ton of smoke."

The fire was contained to one unit, but three units in total were damaged, with one unit below the fire-affected, one damaged by water and one above damaged by smoke.

One person suffered burns and smoke inhalation injuries, according to fire officials, and another person suffered unknown injuries. Both are at a local hospital.

Officials said the cause is unknown, but there were hoarder conditions inside the apartment that caught fire.

The Denver field division of the Bureau of Alcohol, Tobacco, Firearms and Explosives is assisting in the investigation, and the Red Cross is assisting response.

Northglenn police had closed Washington Street to allow fire crews to work on the blaze, but the roadway has since reopened.