An arson probe has been launched into an overnight fire that caused heavy damage to a high-profile cash-for-gold store in the Glencairn area of midtown Toronto.

Emergency crews responded to a call at 2788 Bathurst Street, south of Glencairn Avenue around 2:30 a.m. Monday morning after a TTC driver spotted the blaze.

Crews arrived to find the Harold The Jewellery Buyer store in flames.

The blaze was quickly brought under control, but not before causing extensive smoke damage to the store. Authorities have not released a precise damage estimate.

The cause of the fire has not been confirmed, but one witness said that a Molotov cocktail was thrown into the shop. A tenant living above the shop was not injured in the fire.

Only hours earlier, witnesses said a home near Oakwood and Eglinton Avenues was firebombed. The fires have not been linked by police.

The Ontario Fire Marshal's Office will now probe the case.

The store, which is known to many Torontonians primarily because of its distinctive TV commercials, was in the news last summer when a septuagenarian former employee was charged in connection with an alleged plot to kill rival Omni Jewelcrafters store owner Jack Berkovits.

The plot came to light when the man allegedly hired to carry out the killing met with Berkovits to warn him.

Maria Konstan was arrested and subsequently released on bail.

Harold The Jewellery Buyer's namesake proprietor Harold Gerstel was not charged in the case.

"It's unfortunate, it's very, very unfortunate that people would do these kinds of things, but we're going to be open, like I said, today or tomorrow morning," said Gerstel on Monday.