Up to 25 firefighters are tackling the blaze at the yacht club in Temple Manor Marsh, Knight Road.
It started at around 8pm.
A fire launch boat and the Coastguard are also at the scene.
More top news
Philippa has Friday's weather for the east
Philippa has Friday's weather for the west
Our Olympic heroes will help to create the nation’s biggest ever sports day on Saturday 27 August, with free events throughout the region.