Seven people are still unaccounted for after what appeared to be an explosion in an apartment building in Woodstock, Ont..

With most of the building in rubble, "if we don't have any fatalities, I'll be very surprised," Sgt. Marvin Massecar of Woodstock police said late Sunday afternoon.

Massecar said the building apparently exploded around 8:35 a.m. ET Sunday.

Part of the three-storey building at Victoria Street South and Henry Street is no longer there, Massecar said.

Police had originally thought up to 11 people were missing but lowered that number later in the afternoon.

CBC reporter Gary Ennett reported from the scene that the destruction is "unbelievable," with a third of the building "just gone."

"It's just rubble," he said. "There's no roof. It was blown right off, apparently, and all we have is piles of smouldering rubble."

People in the neighbourhood have gathered around, staring in disbelief, Ennett said.

It is not yet known how many units are in the building or how many people live there.

Heidi Dantes, the director of the ER at Woodstock General Hospital, said she treated seven adults, most for minor injuries. Six of the seven were released and the remaining person's injuries were not critical, Dantes said.

One firefighter was treated for minor injuries.

Woodstock resident Jen Carr said she was awakened by a loud noise, and her house was shaking, so she went to the window.

"I saw ambulances everywhere, people running around," she said. "It was pretty crazy."

Julius Wolf, who lives across the street from the damaged building, said he heard a "terrible explosion" and thought a car had driven into the house or a bomb had gone off.

"The apartment building across the street was just engulfed," he said.

Wolf said he saw a firefighter approach the collapsed part of the building to help a woman when a wall toppled over on him. The firefighter stayed and with the help of another firefighter got the woman out of there, Wolf said.

Debris was blown across the street, he said.

Wolf said he knows people in the apartment building and they are all safe.

Lisa Woods, a spokesperson for Woodstock fire, said the building manager was setting up hotel accommodations for the several dozen residents who have been displaced.

The Salvation Army has set up a canteen at a nearby Via Rail station for emergency workers, while the Red Cross is set up at the Goff Hall community centre. The director of Goff Hall, Bob McFarland, said 100 rooms were also on hold at the Quality Inn.

Len Murphy, president of the local branch of the Red Cross, said the agency would provide food, shelter and clothing for the next 72 hours.

"Nobody's going to be on the street tonight," he said.

Anyone concerned about loved ones should call the Red Cross at 1-866-280-1735.