Nanaimo Fire Rescue responded to a fire at a Husky Gas Station around 3 a.m. Tuesday morning: (Stevie Sawatzky)

Fire investigators are currently on scene trying to determine what caused a fire on the back side of a Husky Gas Station and convenience store in downtown Nanaimo Tuesday.

Crews responded to the gas station fire, located on Terminal Avenue, just after 3 a.m. this morning.

When firefighters arrived, heavy fire and smoke could be seen coming from the back of the building. Firefighters then performed an exterior attack on the fire and contained it to the back side of the gas station.

The store was closed at the time and there were no injuries to report, say fire officials.

While an investigation into the cause of the fire is still underway, witnesses from a hotel behind the gas station told fire investigators they saw flames coming from the building's ventilation ducts and thought it might have been an electrical fire.

A maintenance crew that works for the Husky Gas station tells CTV News that the area of the fire is also known for having challenges with homeless people. A shopping cart, blanket and what looks like discarded needle packages can be seen in the same area of the fire.

Fire officials say that the ventilation ducts are currently too unstable for them to enter to investigate the cause of the blaze. 

Investigators say that a structural engineer and possibly a mechanical engineer will need to be brought in to take apart the building’s heating and cooling system so that an inspection can be safely conducted.

Fire officials say the fire may have started in the building's heating and cooling system, which includes the store’s ventilation ducts. Inspecting this equipment will help determine if a mechanical failure contributed to the fire.

The inspection is expected to take place on Thursday and fencing will go up around the fire scene to secure the area until then. 

The store has extensive fire, water and smoke damage. Nanaimo Fire Rescue says the owner of the business does have insurance and because the fire was contained to the back side of the store, the gas pumps were not at risk.