The Port of Calais has been closed after around 50 migrants reportedly made their way onto a ferry causing a "security incident".
A statement from the Port of Dover said the French port was experiencing "migrant activity" which had caused disruption to services.
It read: "The Port of Calais is currently experiencing migrant activity which has caused disruption to ferry services. Therefore services to and from Calais via the Port of Dover are affected, but DFDS Seaways services are still running to Dunkirk as normal.
"The Port of Dover remains open for business, but the duration of this disruption to services remains unknown."
P&O Ferries Updates tweeted: "The Port of Calais is resolving a security incident. As a result our vessels are subject to delay of between 90 and 120 minutes."