A blaze at a derelict holiday camp near Great Yarmouth was started deliberately, police say.
More than 90 firefighters battled the flames at the old Pontins site in Hemsby, which closed 10 years ago. The reception building was badly damaged.
Norfolk Fire and Rescue Service was called to the Beach Road camp at about 01:20 BST.
It said crews would be there "for some time" and advised people living nearby to keep doors and windows shut.
No-one was injured in the blaze, which is being treated as arson.
Temporary Sgt Hannah Gardiner said: "This incident and our subsequent response did attract public attention and cause concern among the local community.
"I would like to reassure the public we take offences of this nature very seriously."
Following the blaze, Hemsby councillor James Bensly assured people that the town was "still open for business".