A man is dead and a woman is in critical condition in hospital after being exposed to carbon monoxide in their home in Ottawa's east end.

A female friend discovered the couple, both 75, of a bungalow on Phoenix Crescent in Orléans Tuesday morning and called 911, said acting Ottawa police Insp. Francois D'Aoust

"There was a planned outing, a friend attended the residence and found the lady in distress and the male deceased at the scene," D'Aoust said.

Neighbours described the couple as quiet, peaceful and kind, and said they often had antique cars in their driveway. The man who died enjoyed restoring classic cars and showing them, said Sue Schieman, who lives nearby.

She described the couple as "lovely people."

"It's really unfortunate," said another neighbour, Justin Mercier.

Police and paramedics at the scene on Phoenix Crescent on Tuesday morning where a man was found dead and a woman was rushed to hospital. Pets found in the home were unharmed. (Stu Mills/CBC)

First responders arrived at the couple's house at 10:45 a.m. Tuesday.

The female resident was taken to hospital in critical, life-threatening condition and is being treated in a hyperbaric chamber, paramedics said.

Hyperbaric therapy helps to reduce the amount of carbon monoxide in the blood and return a person's oxygen levels to normal as quickly as possible.

The woman who found the couple was taken to hospital as a precaution and is in good condition, police said.

Firefighters said carbon monoxide readings inside the home were extremely high — 600 parts per million with readings closer to 700 parts per million in the basement.

Concentrations above 150 to 200 parts per million can lead to death if a person is exposed over a long period of time, according to the U.S. Consumer Product Safety Commission.

Acting Ottawa police Insp. Francois D'Aoust told reporters the source of high levels of carbon monoxide in the home on Phoenix Crescent is still unknown. (Giacomo Panico/CBC)

Police are investigating source of the carbon monoxide with assistance from the gas company Enbridge along with Canada's Technical Standards and Safety Authority, which oversees the use of fuels such as propane and natural gas.

"Right now we're still in the infancy of the investigation," D'Aoust said.

Police say the poisoning is not suspicious at this time.

Pets found in the home appeared unharmed by the carbon monoxide and were taken by bylaw enforcement officers, said D'Aoust.