Crews responded at about 1:30 a.m. Friday to the 300 block of Grey Street for a structure fire.
Firefighters encountered heavy smoke and flames on arrival.
Crews initially launched an offensive attack but were pulled back by command due to structural instability. Firefighters then switched to a defensive aerial attack.
The structure is connected to a Waterloo Street church property, but the church was not damaged.
This incident comes four days after a former church caught fire, that took place down the road on Wellington Street near Grey Street.
All crews have been cleared from the scene. No injuries were reported. Damage is estimated at more than $500,000.
London Fire crews on scene (Source: London fire department)
