The George in Rye hotel in Rye, East Sussex, which is on four floors with 46 guest bedrooms, had a wedding party in preparing for a wedding today when the fire broke out in the hotel's roof, the fire service said.
Eight fire engines and 40 firefighters were sent to fight the flames at just after 4.30am this morning.
More than 20 guests had to be evacuated.
A spokesman for East Sussex Fire and Rescue Service said: "The crews carried out significant salvage operations to save as many of the guest's belongings as possible, including the bride’s wedding dress.
"In total, eight fire appliances, an aerial appliance and Incident Command Unit attended the fire, support by a full command team, with additional relief crews being required.
"Currently, there are two appliances on scene damping down and turning over whilst the Local Authority Building Control assess the stability of the building structure due to extensive fire damage to the roof."
Due to the age and construction of the hotel, the fire quickly spread through hidden cavities and took hold in the roof void, the spokesman said.
Additional fire appliances, including an Aerial Ladder Platform were sent to tackle the escalating fire, he said.
Incident Commander Dan Channon added: "This was a challenging incident due to the complex nature of this old building in a confined part of the town.
"Crews had to work extremely hard in arduous conditions, using breathing apparatus, to bring the fire under control and prevent it from spreading to other properties."
The cause of the fire will be the subject of a fire investigation, the fire service said.
Staff at the hotel have paid thanks to the fire service for its 'amazing efforts' and said they have been left 'overwhelmed' by support from the community.