Travellers wanting to cross the channel from the UK are facing delays of up to two-and-a-half hours because of an "ongoing inspection" of Eurotunnel.
The latest problems to affect crossings between Kent and northern France come after extra security guards were stationed to try to tackle the crisis in Calais, while David Cameron faces calls to break his holiday and witness its impact "first-hand".
It is unclear whether the current inspection is because of an incursion by migrants in Calais, which have caused major delays to Eurotunnel's summer service and led to nine deaths last month.
A Eurotunnel spokeswoman said: "Service managed to run well last night, but there is something in the tunnel which we need to inspect, which is currently taking place."
She added: "We do have disruption to services, passenger and freight."
From Folkstone there is a two-and-a-half hour wait at the terminal, and from France, passengers are experiencing delays of an hour, as services operate on a single line.
Shadow justice secretary Lord Falconer will visit the French port to discuss the situation with Eurotunnel officials and the Road Haulage Association (RHA).
The RHA urged Mr Cameron to visit Calais and see "the appalling conditions" which lorry drivers are experiencing, as pressure mounts on the Government to secure a long-term solution to the crisis.
RHA chief executive Richard Burnett said: "Without witnessing the mayhem at Calais first-hand, neither the Prime Minister nor his advisers can fully grasp the severity of the situation."
Lorries have repeatedly been targeted by migrants desperately trying to reach Britain.
The crisis is said to have cost the economy millions of pounds as hauliers are forced to dispose of contaminated goods and wait in lengthy queues on the M20 in Kent.
Foreign Secretary Philip Hammond said the Government had "a grip on the crisis" and insisted measures introduced in co-operation with French authorities and Eurotunnel were "already having an effect".
Mr Hammond did not directly address Mr Cameron's absence, due to end on Thursday before he takes further time away from the office.
He added that France and Britain were "determined to work together to lead the campaign in Europe for a more robust approach" to ensuring migrants were returned to their home countries.
A number of measures were unveiled after plans to send extra sniffer dogs and fencing to Calais were labelled a "sticking plaster", including measures to jail landlords who fail to remove illegal immigrants who do not have the right to live in the UK.