An investigation is ongoing  after a small plane crashed into a cornfield in southwestern Ontario, killing all four people inside.

Ontario Provincial Police say a single-engine Cessna 172 crashed around 8:30 p.m. Friday near Moorefield, about 50 kilometres northwest of Kitchener.

 The three men and one woman were pronounced dead at the scene. One of the victims was a 19-year-old woman. The three others were in their 20s, according to police. All are from the Greater Toronto Area.

Curtis Bults was getting ready to leave for a baseball game when heard the plane go down behind his house. ``It sounded like a whiny noise, like a go-kart, like a small plane going 'Eee Eeee Eeeee!,' said the 21-year-old. ``And (then) a couple second delay, and I heard a thud. I heard kind of a shake in the ground.''

Bultz said it took him, his neighbours and emergency crews until 10:30 p.m. before they were able to locate the plane wreckage.

OPP Constable Keith Robb said the plane went off the radar around 8:20 p.m An emergency transponder signal had been activated.

It's unclear how long the plane had been in flight before it crashed. At this point, the investigation remains in its preliminary stages.

`We don't believe weather was a factor,'' said Robb. ``It was a clear, sunny night.''

 Robb said two investigators from the Transportation Safety Board remain at the scene, and were trying to determine whether mechanical failure is at fault. The plane was expected to be removed from the field later Saturday.
 

Bob Connors, the general manager of the Waterloo-Wellington Flight Centre, said the plane was a rental. He said the flight school, which operates out of the Waterloo Region International Airport, had not had a crash like this in a ``long, long, long time.''

Connors would not comment on the experience of the pilot.