The cause of a barn fire near Hensall that killed nearly 1,000 pigs will remain undetermined.

The fire broke out on Fansville Line around 9:15 on Friday morning. The barn was fully engulfed in flames when emergency responders arrived. It was levelled by noon.

Officials say the owner was on site at the time of the fire and found the barn full of smoke when he came out his office, which was also located in the barn.

The barn housed a mix of about 300 sows and 700 weaner pigs, all of which died in the fire.

The owner was treated for smoke inhalation at the scene.

Since the building was reduced to rubble, the cause will likely remain unknown, according to the Fire Chief.