A fire has broken out on the Prague set of History Channel’s “Knightfall,” produced by A&E Studios.

Czech television network CT24 tweeted photos of the blaze, which reportedly erupted on one of the exterior sets for the series, centered around the mysterious Knights Templar. The show is filming at Prague’s Barrandov Studios, with photos from CT24 showing a constructed Medieval castle ablaze, in addition to other exteriors.

A source tells Variety that the fire only impacted exterior sets, and while the full extent of the damage is unknown, it’s believed to be “significant,” with firefighters, ambulances and a helicopter onsite to help control the inferno, according to local reports.

No injuries have been reported so far, although Czech newspaper Hospodarske Noviny reports that three firefighters were treated for fatigue and possible carbon monoxide poisoning after tackling the blaze. The cause of the fire is currently being investigated, with production expected to resume on Monday.

Barrandov is the biggest film studio in the Czech Republic, and one of the largest production facilities in Europe, having played host to the likes of “Casino Royale,” “Mission Impossible” and its later sequel “Ghost Protocol,” “The Bourne Identity,” “Snowpiercer” and many more since construction was completed in 1933.

“Knightfall” was created and is executive produced by Don Handfield and Richard Rayner, with “Avengers” star Jeremy Renner also serving as executive producer for production company The Combine. Executive producers from Midnight Radio are Jeff Pinkne, Andre Nemec, Josh Appelbaum and Scott Rosenberg. Dominic Minghella from Island Pictures is an executive producer and showrunner. Jana Bennett, Arturo Interian and Russ McCarroll are the Executives in Charge of Production for History.