The Office of the Ontario Fire Marshal is investigating after a vacant rowhouse went up in flames overnight.

Toronto fire crews battled a four-alarm blaze through much of Thursday morning after the fire broke out rowhouse on George Street, between Dundas and Gerrard Streets, at about 4 a.m.

The powerful blaze forced firefighters out of the building as it spread to an adjacent home.

No one was injured in the fire, but a number of cats were rescued from the building next door and given oxygen from a specialized animal ventilator.

The building is currently vacant but Toronto fire officials said it was reportedly frequented by squatters.

It is the latest in a series of recent fires that have broken out in the stretch of vacant rowhouses, designated as heritage buildings. A building two doors away from the blaze caught fire last year.

Coun. Kristyn Wong-Tam said the building’s landlord is responsible for keeping the buildings secure, regardless of whether they are vacant.

“A lot of this is reliant on the actions of the individual private property owners,” Wong-Tam told CTV Toronto. “If they don’t secure their buildings and if they don’t make them safe and keep criminals out, obviously we are going to have conditions like this.”

With files from CTV Toronto’s Zuraidah Alman