Two late 19th century homes of great historical significance — both protected under the Ontario Heritage Act and both abandoned pending the appeal of a condo development — burst into flames on Monday after explosions were heard in Wellington and Spadina area.

Toronto firefighters are responding after explosions were heard coming from an abandoned building near Wellington and Spadina - 📹 @martingravel #Toronto #Fire #TorontoFire pic.twitter.com/JjWKXLqIKy

— blogTO (@blogTO) March 23, 2020

Toronto Fire crews responded to 422 and 424 Wellington Street West around 11:30 a.m. this morning, according to officials, for what was deemed a two-alarm fire.

Police say that at least one "small explosion" took place inside the abandoned semi-detached houses.

Heavy smoke was seen pouring from the building's roof and spreading across the city's downtown core as firefighters worked to extinguish the blaze.

Fire at the heritage building on Wellington. Quick response by @Toronto_Fire to get it under control! 👨‍🚒👩‍🚒🚒🙌 pic.twitter.com/92IXMYQ9mg

— quarantine quiche lorraine (@yorkiecult) March 23, 2020

Emergency responders told CP24 that nobody was inside the building at the time of the blaze, though crews have yet to conduct a search and investigations are ongoing.

Firefighters continue to monitor for hotspots as of 2:45 p.m. on Monday, but the bulk of the fire is said to have been knocked out.

Massive ongoing fire at Spadina and Wellington. Explosions can be heard.@Toronto_Fire trucks on the scene. pic.twitter.com/1kH2DMpHsQ

— Saad Khan (@SaadullahKhan) March 23, 2020

The extent of damage to the heritage building is not yet known, but many are saddened by what could very well be the loss of what was once called "The McLeish-Powell Houses."

"Amidst the current chaos, I’m disheartened to hear that the last two houses on Wellington - designated heritage and abandoned pending an appeal of their redevelopment - are currently on fire," tweeted City of Toronto Senior Heritage Planner Alex Corey amid the blaze.

"Happy Monday, everyone."

Amidst the current chaos, I’m disheartened to hear that the last two houses on Wellington - designated heritage and abandoned pending an appeal of their redevelopment - are currently on fire. Happy Monday, everyone. pic.twitter.com/WKsmwb5ijd

— Alex Corey (@acoreyheritage) March 23, 2020

While the cause of the fire is not yet known, Twitter sleuths are speculating wildly as to what may have happened.

"What a coincidence that these two protected properties suddenly burst into flames, paving the way for their development," wrote one.

"Developer arson is always a popular sport in Toronto," wrote another.

"Do we honestly think that developers are arsonists?" ventured another still. "Maybe, just maybe, an old, abandoned house, which likely has squatters, caught on fire accidentally."