Passenger and freight services were delayed on Friday on one of the busiest days for holiday travel.
Eurotunnel said the migrant activity was well organised and planned, with people so desperate to reach the UK they were prepared to throw themselves at trains travelling at 145km/h.
On Thursday, the body of a teenager was found on a train at the Eurotunnel terminal in Kent.
Lorries have been parked on the M20 in Kent for a total of 19 days over the past three months in Operation Stack.
The operation means that lorries waiting to reach France are parked on the M20 in Kent, with the motorway closed to non-freight traffic between junctions eight and 11.
Migrants openly board queued trucks. Photo / EPA
James Hookham, from the Freight Transport Association, said the delays were costing 750,000 ($1.8 million) every day.
"It's a big number and it's certainly of national significance because what is in that queue is the exports of the United Kingdom," he told the BBC.
"It's not just a Kent and southeast England problem. What we're looking at is delays and costs to the whole economy."
MPs, Kent County Council, Kent police, cross-Channel operators and hauliers are discussing how to deal with the disruption.
Damian Green, the Conservative MP for Ashford and former immigration minister, said: "It ought to be possible to protect the Eurotunnel terminal at Coquelles — that is not an impossible policing task.
I know our Government is urging very hard the French Government to meet its responsibilities there."
It is thought there are now about 5000 migrants in Calais.
Hundreds of protesting French sailors earlier this week forced the suspension of Eurotunnel services between France and Britain in both directions after torching tyres on the tracks, causing traffic and travel chaos.
The demonstrations also sparked a scramble among some of the thousands of illegal migrants camped in Calais hoping to reach Britain, as they battled to hitch a ride on vehicles stuck in traffic.
About 200 MyFerryLink workers who had forced their way on to the tracks were later cleared out by French riot police using tear gas canisters.
The sailors, who were from the French ferry company MyFerryLink, were protesting plans by Eurotunnel to sell two of their ferries to rival firm DFDS.
Eurotunnel announced in May it was halting its operational partnership with MyFerryLink due to legal complications, and this month decided to sell its ferries to Danish group DFDS.
