People are being told not to worry if they see an increased emergency service presence at the Elizabeth Terminal.
Jersey's government is practising the response to a major incident with 'live incident' at the harbour from 9:00 am until 2:00 pm today (8 October)
The Jersey Resilience Forum - which includes Ports of Jersey, Customs and Immigration and all emergency services - will be involved.
Exact details of the scenario have not been released, but it will involve setting up a 'Survivor Reception Centre'.
Volunteer actors are being used to play the part of distressed victims who look like they need medical attention.
Officials want to reassure people that it is just part of the exercise.
The terminal will be closed to the public at 8:30 am, but no passenger sailings are scheduled so there will be no travel disruption.

Channel Islander abandons Bordeaux as the flames 'arrive at the city's gates'
Nowacki wins Jersey’s first Commonwealth Games medal in 36 years
Thousands expected at Havre Des Pas Festival this weekend
Commonwealth Games: Nowacki into 100m breaststroke final
Channel Islands face 'physical' Poland test
Price of heating oil and other fuel increase by more than half in a year
Man jailed for importing nearly £600k worth of cannabis in bumpers of his car
Baby born on Guernsey's Marine Ambulance