Investigators have identified a woman and child who plunged to their death off a Toronto highway overpass.

Andrea Johnson, 30, died of multiple trauma. The boy, two-year-old Sulla Genua, succumbed to blunt impact head trauma.

They had landed onto the busy Highway 401 beneath the Morningside overpass in the city's northeast at about 7:15 p.m. Sunday night.

Johnson was reportedly struck by several vehicles before traffic came to a standstill.

Ontario Provincial Police Const. Dave Woodford was shocked by the gruesome scene.

"I've seen some really horrific things in my career, but I don't know about something like this with a child," he said.

Johnson died at the scene, her body broken into separate pieces. Her son was rushed to hospital but died en route.

Investigators are treating the incident as a murder-suicide. Police said several motorists stopped and spoke with Jones after they noticed her on the overpass.

Despite their efforts, she jumped anyway.

Several witnesses were taken by Toronto police to the nearby 42 Division station on Milner Avenue for questioning.

People leaving a nearby shopping centre flocked to the area, shocked by what had happened, CTV's Carol Charles reported.

"You never want to see these things happening, and you never want to see it happen to anyone. And to a little kid ...," one bystander said.

Knowing the symptoms

Experts say it can be difficult to recognize the signs that a person is thinking about suicide or worse.

Dr. Ariel Dalfen told CTV News that it is very hard to predict a dangerous situation unless a person is "very intimately involved with the family."

But Dalfen said that there are "a few factors" to watch for.

"The first being, what's going on in this woman's life? Is she being abused at home, is she being threatened in some way on the home front that could make her so distraught that she feels that she has no other options," Dalfen said Monday.

She added that sometimes mental illness plays a role.

"Is she severely depressed and feels she has no other options? Or is she somehow psychotic, meaning she has lost touch with reality, hearing voices telling her to do this, hearing voices to end her life and the life of her child?"

Dalfen recommends people contact crisis intervention centres or their family doctor if they are experiencing these feelings.

With reports from CTV's Carol Charles and Chris Eby