A police officer responding to assistance at a vacant apartment Monday morning in a southwestern Ontario city was hit by three flying butter knives, believed to have been set as a booby trap.

"It wasn't a sophisticated setup, but there's no doubt that the person who set it up intended to harm whoever opened the door," said St. Thomas Police Const. Tanya Calvert.

A senior officer was called by a landlord to an apartment in St. Thomas. The landlord believed an evicted tenant was trespassing and wanted police help, Calvert said.

Flying knives are not something that we've dealt with on a regular basis. - Const. Tanya Calvert

When the officer arrived, the landlord unlocked the door but it wouldn't open.

"It's barricaded somehow. The door is resisting being opened. He's not sure if there's furniture up against it or what, but he opens the door with some force only to have these three knives come flying at him," Calvert said.

"The knives were jammed up in the doorway, so when they did release, it was with quite a bit of velocity, so they did hit (the officer) with quite a bit of force."

The officer was struck in the hand and in the chest. The third knife missed both the officer and the landlord and landed on the floor.

Calvert said, had the officer been struck in the eye, it would have resulted in a serious injury. She added that the officer's training likely prevented injury.

"We're trained, when we open the door, we back out, to be ready on what's on the other side of the door. That's why the knife didn't hit him in the face," she said. "When it happened, it was a good reminder for all of us to always be aware and never get complacent."

"Usually, we anticipate a dog or something along those lines. Flying knives are not something that we've dealt with on a regular basis."

Calvert didn't want to discuss the specifics of the booby trap setup because she didn't want to give anyone any ideas.

"Looking back we can have a bit of a laugh, but at the time, it wasn't funny. We're thinking, 'What else is in this apartment?'

St. Thomas police are investigating the incident and could lay charges, she said.