Officers are probing an apparent murder-suicide north of Toronto which has left a mother of two and her estranged husband dead.

Witnesses in Orangeville say the woman, identified as 39-year-old Heidi Ferguson, was shot in the chest before she pleaded for help at a neighbour's home around 1 a.m. Saturday.

While she lay dying, Ferguson reportedly told the neighbour: "I've been shot by my husband ... please help me."

As she was airlifted to Toronto's Sunnybrook Hospital, clinging to life, police descended on her husband's million-dollar home in Mono Township, about 13 kilometres from where the shooting occurred.

What followed was a standoff between 42-year-old Hugh Ferguson and tactical police. A short time later, officers entered the home to find the man dead, reportedly from a self-inflicted gunshot wound.

Heidi Ferguson, an interior designer and local businesswoman, had wanted a fresh start in life after separating from her husband, friends say.

She had been renting the Orangeville home and was looking to move on without her husband, who was her business partner in a renovation and interior design company.

Friends said that the husband was attempting to reconcile just before the deaths.

On Sunday, the spacious Mono Township home which she had shared with her husband and two children -- a son aged 15 and a daughter aged 19 -- was cordoned off with police tape as officers searched for clues.

Residents who lived next to the family were shocked by the events.

Orangeville neighbour Danny del Zotto said the children are also victims in the deaths.

"It's a terrible thing for something like that to happen to them. And now they have no parents. That's just terrible," del Zotto told CTV Toronto.

While the chain of events which led to the deaths appears to have been pieced together, the Special Investigations Unit is looking into what occurred during the critical hours before the shooting.

According to the Ontario Provincial Police, officers were called to the woman's Orangeville home late on Friday after receiving reports of a heated fight between the couple.

Though officers responded to the call, they left the scene after a short time because the husband had fled.

However, less than an hour later, police were back on the scene after a gunshot was fired.

The SIU is called in when police are involved in a death or serious injury.

With a report from CTV Toronto's Jim Junkin