Firefighters spend more than 1
Crews were called on the site at Leavesden, Hertfordshire, at 23:29 BST on Wednesday.
The council said that the set involved was not used at the time and no damage was reported.
All eight Harry Potter films as well as other films including James Bond, Fast and Furious and the Mission Impossible franchise has been captured in the studios.
Fire service confirmed shortly before 15:00 BST the fire came out, although some crews were still at the scene.
A spokeswoman for Warner Bros will not comment on the blaze, except to confirm that the public studio tours are unaffected and are occurring as before.
Mark Hancock, who lives nearby, said: "My house is about 200m away from the grounds and there is a clear line of sight in the gardens so we went to one of our windows.  "The smoke was raised in the air, and as I watched, the smoke appeared to get thick, so much so that we could see the flashing lights of the fire engines emitting thick smoke.
"It's still still strong at about 1:00 and when I wake up in the morning it's still smoldering."
He added there was a "strong smell and flavor of smoke in the air".
On the scene: Alex Pope, BBC News
As the studio is a closed set no one can get close to the scene.
The studio backs on a housing estate from which you can smell a faint burning odor.
A woman who lived there said I was awakened by a strong odor at about midnight and her dog was barking and "she did not barks".
"The smell was so strong that I thought it was coming from home," she says.
Another resident said he spoke to a firefighter this morning telling him that it was "a big fire."
A spokesman for the Hertfordshire Fire and Rescue Service confirmed that 15 crew were sent to the scene when the fire exploded. Later reached 18.
He said an aerial ladder was used as well as 12 sets of breathing equipment.
Police also needed to close the Bridge Road to Leavesden to allow the fire service to run a hose from the nearby canal to the fire site at its height.