The United Nations has called on France to introduce a "civil emergency" plan to deal with the thousands of migrants camping in Calais in the hope of reaching Britain.
Vincent Cochetel, head of the UN refugee agency's Europe division, called for an "urgent" response to the crisis - which has so far seen nine people die during the attempted crossing.
He also called on Europe to "wake up" to the wider crisis across the continent, referencing the struggle faced by Greece in dealing with the huge number of people arriving on its shores via the Mediterranean Sea.
The warning comes amid reports the British government is considering the "nuclear option" of closing the Channel Tunnel overnight in a bid to prevent people from trying to enter.
A Sudanese man was arrested at the Folkestone end of the tunnel on Tuesday after allegedly walking almost its entire 31-mile length in a bid to get to the UK.
A joint police operation has been launched to target people-smugglers who profit from the desperate migrants trying to reach the UK.
Calais' Mayor has accused Cameron of treating the region with "contempt" - and called on authorities to open the border unless help is given
More fencing and extra sniffer dogs have been sent from the UK to Calais in a bid to curb migrant incursions into Britain.