By 8.00 a.m. BST (2 a.m. ET) 15 fire crews were at the blaze, which was first reported at approximately 11.30 p.m. BST, officials stated.
A fire has broken out at Warner Bros studios, the famous filming location in which Harry Potter was filmed.
Update: Firefighters have now put out the blaze that broke at Warner Bros. studios in Leavesden overnight.
A spokeswoman for Warner Bros Studios said earlier that the studios and tours were open.
Original story: 18 fire crews and around 75 fire fighters are now tackling a blaze at Warner Bros studios in Leavesden, after a fire broke out last night.More news: Star Wars: The Rise of Skywalker New Sith Trooper Revealed
"Fire and Rescue Service were called to reports of a fire at Warner Bros Studios in Leavesden at 11.29pm on Wednesday, 10 July", said a spokesperson for Hertfordshire County Council.
Hertfordshire County Council's Fireplace and Rescue Service stated that "the set was not getting used on the time of the hearth" and "there are not any accidents".
Leavesden is well known as the home of the Harry Potter franchise and has also housed James Bond movies, the Fast and Furious franchise and Mission Impossible movies.
The studio, which occupies a sprawling complex in Leavesden, offers popular tours of the sets and sound stages used in the Harry Potter films.
The incident began late on Wednesday evening, with nearby residents seeing smoke rising from the lot.More news: Couple claims clinic implanted their embryo in wrong woman
He also said a "strong smell and taste of smoke" filled the air.
A spokesman for Warner Bros did not comment on the fire but told the BBC that public studio tours were unaffected and taking place as normal.
More as we have it.
"It was still going strong at about 1am and when I woke up this morning it was still smouldering".More news: Trump directs government to revamp care for kidney disease