Eurotunnel day trip passengers told to postpone journeys
Passengers on Eurotunnel day trips to France have been advised to postpone their journey if they can following further disruption.
The Foreign Office has also warned travellers about industrial action and migrants in Calais.
In Kent, lorries are queuing to cross the Channel on the M20.
Operation Stack, where lorries waiting for crossings have to park on a closed section of the motorway, is now in place from junctions 8 to 11 on the coastbound M20.
Junctions 12 and 13 are also closed to help with traffic management in the area but not to queue lorries, and only tourist traffic for the Channel Tunnel is allowed to join at junction 11.
Kent Police said Operation Stack was expected to remain in place into Wednesday.
The latest M20 closure comes amid a row about a proposed contraflow system that was suggested as a way to keep the route open while Stack was in place.
Kent Police said the emergency measure had been brought in because of a large amount of freight heading towards Dover and Eurotunnel and continued disruption in Calais.
Home Secretary Theresa May earlier met her French counterpart to discuss the ongoing disruption.
A government spokesman said it was continuing "to work very closely with the French authorities over the need to stop blockades and maintain port security.
"There does remain a possibility of further disruption and travellers should check travel advice with their operators," he said.
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Both the Port of Dover and P&O Ferries have said they remain open for business.
In a statement, the Port of Dover said: "The port and the ferry operators are together working hard to serve all customers travelling to and from the continent.
"We apologise for any delays or inconvenience as a result of traffic congestion."
P&O said it was aware of Foreign Office advice and it wanted to make clear that Calais at present was both safe and open for business.
P&O's commercial director Janette Bell said traffic could access the Port of Calais freely and cars and lorries were queuing safely and efficiently.
She added: "There is no point at which illegal migrants come into contact with our passengers."
DFDS Seaways had suspended its crossings on the Dover-Calais route because of an incident with a flare, but resumed the service on Tuesday.
Foreign Office advice to passengers is to check with operators and plan journeys to avoid disruption.
It has warned of industrial action by farmers, continuing strike disruption to cross-Channel services and large numbers of illegal migrants.