Scenes of hundreds of migrants in Calais trying to board lorries to the UK during a strike were “totally unacceptable”, PM David Cameron says.
Ministers said a “significant number” of would-be migrants had been stopped during the French ferry worker strike.
Mr Cameron told MPs it was important to work with France to tackle the problem and warned against “either side trying to point the finger of blame”.
Cross-Channel transport is returning to normal although there are delays.
Ferry, Eurotunnel and Eurostar services are running mostly to schedule, but those delayed on Tuesday face waits to rebook trains.
The M20 in Kent is closed between junctions 8 and 9 as parts of the motorway are used to create a queue for lorries heading to the continent. The operation will last for the rest of Wednesday, Kent Police said.
Mr Cameron said more needed to be done to tackle the issue of migrants trying to cross the channel to the UK, but the strike had played a “key role” in Tuesday’s events.
He said the UK government wanted to see better documentation of migrants coming into Europe via the Mediterranean.
The PM said he had discussed putting more border staff and sniffer dog teams in Calais.
He added ministers needed to act to:
Ensure better security at Calais, in co-operation with French authorities
Work with European partners to stop the problem “at source”, breaking the link between travelling to Europe by boat and “getting settlement” in Europe
Make sure Britain is a “less easy place for illegal migrants to come to and work in”
Home Secretary Theresa May, meanwhile, said the UK Border Force had put in place “tried and tested” contingency plans.
She said: “Despite the extra pressure caused by the French strikers, Border Force maintained border security by following plans to put additional staff in place to search freight vehicles passing through the affected ports.”
The story of Calais is an enormous headache for the prime minister and it couldn’t have come at a worse time.
Just as the prime minister is about to formally table his proposal to re-negotiate Britain’s relationship with the EU at a leader’s summit he is confronted by images that highlight the issue that does the most to alienate voters from Europe – immigration.
Shadow immigration minister David Hanson said it was important French authorities “take further action to ensure they support” the UK in humanitarian efforts and ensuring the “integrity” of its borders.
The government also said a taskforce to tackle organised immigration crime in the Mediterranean is being set up. Many of the migrants at Calais are believed to have crossed the Mediterranean in boats run by people traffickers.
Migration is also due to discussed at a two-day European Council summit in Brussels, which begins on Thursday.
Police in France said 350 migrants had been found in cars and trucks between 06:00 and 10:00 on Wednesday morning.
Eurotunnel said migrants had continued attempting to get on to trucks slowing down on the outskirts of Calais on Wednesday.
And seven people were arrested in Bedfordshire earlier on immigration offences. They were all detained near the Northbound M1 services at Toddington.
Abdul Aziz, 22, originally from Sudan, told the BBC he had travelled to the UK from Calais on Wednesday by clinging to the underside of a lorry.
On Tuesday, Eurostar tweeted that a fire caused by striking ferry workers had damaged the track, leading to all trains being cancelled.
It says services are now running on time, and passengers whose trains did not run are being asked to exchange their tickets – though they will not be able to travel until the weekend.
Eurotunnel, which manages the Channel Tunnel and runs car-carrying trains, says services are now “operating to schedule”.
Ferry services have also resumed, though there are some delays.
HGV driver Andy Wilson, who was stuck on the UK side of the Channel on Tuesday, told the BBC his working day was “virtually destroyed”.
He added: “When you’re driving in toward Calais there’s hundreds of migrants just waiting for you to stop.”
One migrant at Calais, Moaz, said life in France was “difficult” and he believed he could get a home in England “very quickly”.
A Sudanese man told the BBC he had heard Britain would not “leave you” to live in a camp like the one he lives in near Calais port.
“They will receive you with food… house, then after that you will get a chance to ask for asylum,” he said.
About 3,000 migrants are estimated to be living rough around Calais, waiting for a chance to cross the Channel.
On Tuesday Philippe Mignonet, a deputy to the mayor of Calais, said French people were “fed up” and Britain must “take responsibility” for policing its borders.
“You’re on an island and you can’t see that it’s your problem to deal with your security. I’m sorry to say so – it’s your security,” he told the BBC.
The Home Office says about 19,000 attempts to cross the Channel have been prevented so far this year, more than double the number during the same period last year.
The new Mediterranean taskforce to be announced later is a 90-strong law enforcement team including staff from the Border Force, the National Crime Agency, Immigration Enforcement and the Crown Prosecution Service.
A handful will be based with Europol in Sicily and the Hague, in the Netherlands, with most on deployment standby in the UK.
The UK had already announced extra security measures at ports in northern France and Belgium, where UK Border Force staff work alongside national authorities.
The measures include:
a £2m upgrade of detection technology
£1m extra for dog searches
£12m over three years into a joint fund with France for security at Calais port
new fencing in Calais to “enhance security at the port and help protect traffic on the road leading to it”