One of the owners of a midtown Toronto house flattened in an explosion is missing and crews have begun searching for her remains in the debris.

Jyoti Moorthy lived at the upscale house with her two young sons and husband, a University of Toronto professor, and has not been seen since the explosion late Wednesday morning.

Debris is all that remains of the three-storey house on Harper Avenue.
(Geoff Ellwand/CBC)

"At this stage we are going to start moving forward to a recovery situation," Toronto police Det. Murray Barnes told reporters. "We do believe at this point she may well still be inside the house."

He says the incident is being treated as a tragedy.

Investigators will spend the day sifting through the charred remains of the three-storey home on Harper Gardens, near Mount Pleasant Road and St. Clair Avenue East.

"It is devastating. There was nothing left down there," said Barnes.

An Enbridge gas serviceman, who was working in the house at the time, survived the blast thanks to neighbours who pulled him from the wreckage. He suffered second-degree burns and is still in hospital in serious but stable condition.

Firefighters spent much of Wednesday waiting for natural gas to be shut off in the area, a troublesome task because of the frigid temperatures.

Two neighbouring houses were damaged by fire. About a dozen people were temporarily removed from their homes as a safety precaution.

Ontario's fire marshal has been called in to investigate. Fire officials have said they suspect a gas leak.