Eurotunnel is poised for another difficult night after around 150 migrants tried to storm the Channel Tunnel terminal in a bid to board UK-bound freight trains.
Services were delayed and cancelled after migrants accessed restricted areas on the French side, said the Chunnel operator, which has reportedly increased security.
The migrant crisis has escalated in recent weeks in Calais, with around 3,000 people displaced from countries including Eritrea, Syria and Afghanistan setting up camp near the port.
Amid mounting calls for a solution to be reached, Keith Vaz, the Home Affairs Select Committee chairman, visited Calais and met its deputy mayor Philippe Mignonet.
Mr Vaz told BBC News: "It is a very difficult situation and it is getting worse. If you get a thousand migrants being taken out of lorries every single day, then you really have a big crisis.
"They (the French authorities in Calais) are certainly under-resourced. They claim to have 600 police officers here but they need much more.
"They need to make sure that when they find the migrants, they are finger-printed, they are processed and therefore they are then returned to their country of origin. That is the only way to deal with this issue.
"You have to separate those who have actually paid to come from the genuine people who are seeking asylum and this is not happening.
"The numbers have doubled over the last year, they are going to get worse over summer and at night the situation is intolerable.
"Something really does need to be done - by the EU, by the French authorities - in order to make sure that this is stopped."
The latest incident caused the return of queues on the M20 in Kent for lorry drivers trying to cross the Channel after police reintroduced Operation Stack, which was later lifted.
It came in the week that more than 3,000 truckers were forced to queue for several days in high temperatures on the M20 following a wildcat strike by ferry workers in France.
All phases of Operation Stack had only been lifted for a matter of hours before the migrants attempted to storm the terminal on the French side.
Added to the problems was a temporary technical issue in the tunnel, which impacted on passenger services, causing two-hour delays from the UK and 90 minutes from France.
Kent Police said the M20 had now fully opened but a force spokesman warned drivers to be aware of "residual delays" while the tailbacks cleared.
The bold attempt by migrants to storm the terminal led to renewed calls for authorities to act to solve the worsening crisis, which is costing the UK economy millions of pounds.
The Fresh Produce Consortium estimates that £10 million of fresh fruit and vegetables have been thrown away since the start of the year as a result of the problems in Calais.
Dan Cook, operations director of Europa Worldwide Group, a transport, distribution and logistics firm, said "marauding mobs" were effectively halting British trade to the continent.
He said: "We have had vehicles on the motorway in broad daylight being surrounded by marauding mobs racing around, opening doors, cutting trailers, climbing into the back.
"We have experienced quite a bit of theft and damage to customers' products. You're looking at not only the damage to equipment but also claims from customers as well.
"On Wednesday, we had a trailer on the motorway where migrants climbed in through the roof at 4pm, and it had a full load of fashion retail.
"It looked like a bomb had gone off. The whole load had been spoiled.
"And then there's the sheer intimidation to drivers. It's a very, very intimidating situation - you're a sitting target, with people running around trying to climb on.
"The fundamental problem is that there is no sign of any active policing to stop this happening in Calais. There is no security from the army, police or whoever to protect what is the gateway to trade."
Mr Cook said this week's disruption has cost his firm about £100,000, adding: "For a medium-sized company like ours, that's unsustainable."
He said the French authorities needed to provide adequate security to allow drivers to pass through the key trade route to the continent.
Mr Cook added: "I don't believe that in 2015 we should accept mobs just stopping trade moving from one place to another. I think there is a duty of care."
Dover Conservative MP Charlie Elphicke said the problems underlined the need to consider expanding the port at Dunkirk, 45 miles from Calais.
Migrants have been taking advantage of slow-moving and queuing traffic by trying to board UK-bound vehicles, forcing some drivers to take long detours to skip Calais altogether.
Following the latest incident, a Eurotunnel spokesman said: "Eurotunnel reiterates its call to the authorities to provide a solution to the migrant crisis and restore order to the Calais region."
Home Secretary Theresa May and her French counterpart Bernard Cazeneuve this week agreed to increase the joint intervention fund to improve security around the port and the Channel Tunnel.
French aid workers have reported a "catastrophic" situation, with predictions that 2,000 more migrants could arrive over the summer at the camp, dubbed Jungle II.
Volunteers from l'Auberge des Migrants say up to 50 new migrants were arriving every day at the camp, and there were not enough tents, blankets or food.
Kate Gibbs, of the Road Haulage Association (RHA), said the economic impact of the repeated disruption in Calais was "horrendous" as she praised British truckers for their resilience.
She said: "This situation cannot continue because it's putting hauliers at risk, in terms of their lives and their livelihoods.
"We have got to see an urgent solution. Right now, we need a short-term fix, but we have also got to work on a long-term solution.
"We have heard stories of drivers being threatened with knives. What I cannot stress enough is that these truckers are not getting the recognition they deserve.
"They are doing a fabulous job for the haulage industry, and the supply chain relies on them. Every member of the public relies on HGV drivers.
"Profit margins are so tight in the industry, between 2% and 3%. One guy I spoke to who was driving a refrigerated lorry was trying to get meat to France.
"As he got stuck in Operation Stack, it meant the shelf life of his products was greatly reduced. The French don't see it as their problem but we have got to see action.
"If it means calling in the French military to support the police, then so be it."
The Port of Dover, which faced heavy disruption this week due to striking ferry workers in France, said it remained "open for business" despite the problems with the Chunnel.
A port spokesman said P&O Ferries was operating a full Dover-Calais service while DFDS Seaways was running full services to Dunkirk.
A Home Office spokesman said: "Law and order in and around Calais is the responsibility of the French authorities, but the UK continues to work with its French counterparts to strengthen the security of the border to stop illegal immigrants entering the UK.
"Earlier this week the Home Secretary and the French interior minister agreed to increase the joint fund which has already allowed for the strengthening of security at the Port of Calais and which will reinforce security at the Channel Tunnel.
"Alongside this resolute action we are also tackling the roots of this problem by increasing joint intelligence work with the French to target the organised crime gangs."