No injuries have been reported, and the fire is said to have started on a sound stage not now in use.
Warner Bros described the alleged attack as an "isolated workplace incident" in a statement issued at the time.
Fifteen fire engines were at the Leavesden studios in Hertfordshire where the fire started late on Wednesday night, the local council said.
"Fifteen fire engines, plus support vehicles, are now in attendance at the scene and crews are tackling a fire in one of the stages there".
"The set was not being used at the time of the fire". There are no injuries.
In addition to being the studio the place all eight Harry Potter motion pictures had been made, motion pictures like Christopher Nolan's The Darkish Knight, Mission: Inconceivable - Fallout and Spider-Man: Far From House had been additionally filmed there. "When I woke up this morning it was still smoldering and when I left for work this morning, there was still a strong smell and taste of smoke in the air".
The studio began life as an aircraft factory during the second world war but was converted in 1994 at the behest of producers on Bond movie GoldenEye.
A fire has broken out at Warner Bros studios, the famous filming location in which Harry Potter was filmed.
Guests today have been told tours are still going ahead and to turn up as normal.
A couple of photos taken during the night show a huge plume of smoke over the studios.
It's not year clear how the fire first erupted but reports have confirmed public studio tours are "unaffected" and will be continuing as usual.
Yahoo Movies UK has contact Warner Bros for comment.