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.
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Student Charlie Mann was jailed for 16 months for the attack on his mother at their family home while high on Meow Meow.
Monday night's weather for the east of the region
Monday night's weather for the west of the region