Officials are investigating the cause of a three-alarm fire at a vacant building in the city’s downtown core this morning.

The fire broke out at a boarded up building on Wellington Street, near Spadina Avenue, shortly after 11:30 a.m.

Toronto Fire Services says there were also reports of explosions at the site.

It does not appear anyone was inside the building at the time.

Firefighters were on scene for several hours Monday monitoring hotspots.