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Work begins on the second deck for the car park at Medway Maritime Hospital on Monday.
The project is expected to take six months, during which heavy plant will be operating on the site.
A spokesperson for Medway NHS Trust said there would be unavoidable disruption while the work is carried out.
People visiting the hospital should arrive early in case of delays in finding a parking place.
Arrangements are being to ensure some parking on the Hospital site although capacity will be limited.