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Capacity at Fleet's stadium is set to rise back above 4,000 when a stand refurbishment is complete.
The work means The Swanscombe End at Ebbsfleet United's Kuflink Stadium, in Stonebridge Road, will be closed until further notice.
The emergency exit stairs at that stand have been removed already before the main phase of work begins.
Supporters may still enter the ground via the turnstiles at the car-park end but there will be no access to the fenced-off terracing.
A statement on Fleet's website read: "The club appreciates the co-operation of all supporters as we embark on this vital project to bring our capacity levels in line with appropriate limits. We have opted for January to minimise any inconvenience in a very tight schedule for completion."