The Ottawa police arson unit says it appears two overnight fires near the Central Experimental Farm were deliberately set and related to each other.

Several 911 callers first reported hearing an explosion and seeing flames around 11 p.m. Monday at 920 Dynes Rd., a series of rowhouses not far from Prince of Wales Drive.

Then, about an hour and a half later, another explosion and flames were reported at an unoccupied house at 1077 Dynes Rd., closer to Fisher Avenue.

View a map of the two fires here.

Before investigators started to sift through the ash and rubble at the rowhouse later Tuesday, Sgt. David Christie of the Ottawa police arson unit said it appears likely that the two fires are linked, and that they were deliberately set.

"You have two fires both occur within a short distance of each other, right around the same timeframe, it's highly unlikely you'd have two accidental fires starting in that manner," he said.

"Also there's some information about possibly a person seen fleeing the scene."

Investigators from the Ottawa police arson unit and Ontario Fire Marshal's office sift through the debris after a fire at a rowhouse at 920 Dynes Rd., near the Central Experimental Farm. (Andrew Foote/CBC)

Paramedics treated two patients from the first fire:

A 20-year-old man suffered second-degree burns on his upper body, paramedics said, and his airway was also hurt.

A 27-year-old man suffered burns on his face and chest.

Both were taken to hospital in serious but stable condition. One may need to be taken to a specialized burn unit in Toronto, Christie said.

Officials from the provincial Fire Marshal's office are also investigating due to the serious injuries sustained by the two burn victims.

'I heard a loud boom'

Sarah Hogan, who lives in the area, was walking home from a friend's place when she heard a possible explosion coming from the rowhouses.

"As I was walking from Dynes toward Prince of Wales I heard a loud boom, and was kind of startled by it. I looked behind me and I could see flames coming from the houses on Dynes Avenue," Hogan said in an interview Tuesday.

She estimates she was about half a block away when she heard the possible explosion, and said she went home to grab a camera to take pictures and talk to neighbours.

"You couldn't ignore the fire trucks, the paramedics, the police driving by with their sirens on. ... It was a bit startling, hearing all the sirens," Hogan said.

Several people were displaced from the rowhouses, and firefighters said the Salvation Army and Red Cross were called in to help them. The people right next door to the badly damaged unit shouldn't be displaced too long, Christie said, although their home was damaged by the flames.

The people two doors over should be able to return soon, he added.