Seven residents of a Woodstock housing complex are missing after an early Sunday morning explosion and fire.

Neighbours reported hearing a loud explosion around 8:30 a.m. at the apartment complex on Victoria Street South. "I had just got up to text my daughter-in-law, when our bedroom wall literally exploded," said resident Cindy Gale. "Everything that was on it was flying."

Fire crews, Oxford EMS, police and air ambulances were called to the scene. When they arrived the roof of the building was on fire and thick smoke filled the air.

"They were screaming at [one resident to] get on the ladder," said neighbour Tanis Sloat. "All of the sudden right behind them in that apartment… it just went up in flames… the whole apartment."

The first priority was to locate all residents in building, but that made it difficult to fight the fire.

Deputy Chief Brian Arnold said that "during that time frame there's a degree of fire control going on, but not as much as you would anticipate having for such a large structure fire."

Firefighters battled the blaze for hours until it was finally extinguished. At one point the centre of the building collapsed, making it unsafe to continue further search efforts.

Seven people were taken to hospital by Oxford County EMS. Six were treated and released; one remains in hospital with non-life threatening injuries. A Woodstock firefighter was also taken to hospital with minor injuries.

Police are unsure whether the seven people unaccounted for were in the building at the time of the fire.

Residents were evacuated from the 45-unit complex and relocated to the Finkle Street community complex.

Family members who are trying to locate loved ones are encouraged to call Red Cross at their toll free number: 1-866-280-1735.

Both the Ontario Provincial Police and Fire Marshall's Office have been called in.