Gunfire and explosions at the Port of Dover later are part of a major drill designed to test the reactions of the emergency services.
The exercise will force the port to shut from midnight tonight until 5am on Sunday.
The major live multi-agency exercise, the final one of three, is going ahead to ensure the port and its partners are ready to deal with a variety of possible emergency situations.
Port authorities warned that mock explosions or sounds of gunfire may be heard, but have reassured residents there is no cause for alarm.
Port chief executive Tim Waggott said: “Such exercises, which we conduct from time to time with our partners, are extremely important in ensuring that we proactively prepare for any eventuality.
“As Europe’s busiest ferry port, it is vital that we keep the safety and security of all those who work in and travel through the port at the forefront of our operations.”
Superintendent Andrea Bishop of Kent Police said: “Dover is the gateway to the UK and Europe and one of the world’s busiest ports. Consequently, it’s of huge strategic importance.”
She added: “Keeping the port safe and secure for the millions of people who travel through it or work there is a priority for us and our partners.
“Kent Police has the expertise and resources to ensure that people can go about their business safely, but it’s important that we periodically put those to the test.
“Such exercises are vital to make sure that we can effectively and professionally deal with potential incidents in the best way possible”.