Four people, three of them pro-migrant activists, were arrested Monday and 11 police officers suffered minor injuries when police began dismantling structures in the "Jungle," the sprawling camp near the northwestern port of Calais, authorities said.
Calais authorities plan to demolish the southern half of the camp and relocate the inhabitants in response to unsanitary conditions at the site, but met stiff resistance from some migrants and supporters from pro-migrant activist group No Borders Monday.
Tents were set on fire and projectiles were thrown at police at the site, resulting in arrests and injuries and prompting authorities to use tear gas, Steve Barbet, spokesman for the Calais prefect, told CNN. Later in the evening, protesters and migrants blocked the city's perimeter highway, throwing projectiles at trucks to slow them down, he said.
Calais, the closest French city to the UK, is a major port where ferries cross the English Channel and is situated clos e to an undersea tunnel connecting the two countries. The "Jungle" is a major transit point for thousands of migrants hoping to enter the UK illegally.
Cazeneuve labels activists 'violent' militants
French lnterior Minister Bernard Cazeneuve said in a statement Tuesday that the government remained committed to the safety of the migrants at the camp, and vowed to push ahead with the clearance.
"The activism of a few No Borders militants, radical and violent, cannot stop it: This operation will go on in the next days, with calm and discipline, and will offer each and every (migrant) a spot as the government promised," he said.
The clearance had begun peacefully Monday morning, the statement said, until No Borders activists began to "harass" social workers informing migrants of their relocation options.
Fabienne Buccio, prefect of the Pas-de-Calais region, told reporters last week that the Jungle would be dismantled peacefully, without the use of force, over a period of several weeks. The clearance would be carried out in cooperation with charity associations which would encourage migrants to move voluntarily to the better-equipped facilities, she said.
The work was delayed until a legal appeal against the plan by migrant charities was rejected by a French court on Thursday.
Help Refugees, a charity which works in the camp, accused French authorities of breaking their promise that the clearance would be "gradual, humane and respectful of the dignity of the people living in the camp."
"The scenes of panic we witnessed today were a far cry from these principles," the group said in a statement.
Calais authorities say that buses are on site at the camp to take migrants to reception centers.
But many are reluctant to leave the camp, because the UK, not France, is their desired destination. Help Refugees said neither of the two 50-seat buses at the camp on Monday was full by the time it left for the reception centers.
UNHCR: 'Imminent humanitarian crisis'
Europe is struggling to respond to a massive influx of migrants, many of them refugees fleeing the war in Syria, but hailing from other troubled countries as well.
The United Nations High Commissioner for Refugees warned Tuesday of an "imminent humanitarian crisis" in Europe as countries remained at odds over their response to the issue.
Austria and countries along the main Balkan migration route through Europe -- including Slovenia, Croatia, Serbia and Macedonia -- recently agreed to tighten border controls to slow arrivals to a trickle.
The move has created a rapidly growing bottleneck of migrants in Greece, a country facing its own severe financial hardships, as the flow of people there from Turkey continues unabated.
Numbers mount up on Greek-Macedonia border
Tensions boiled over on the border of Greece and Macedonia Monday, when scores of migrants rammed through a barbed-wire security fence, prompting authorities to use tear gas in an attempt to keep the crowd at bay.
The incident happened at the Greek village of Idomeni, a main transit point for refugees traveling to western Europe, where numbers of migrants have quickly backed up as Macedonia refuses to allow them to enter.
Dejana Nedeljkovic, chief public relations adviser at the Macedonian Interior Ministry, told CNN that only Syrians and Iraqis with photo IDs were being permitted across the border, and only in numbers that were within the capacity of transit camps in countries along the route, and in destination countries.
Migrants ram the border fence between Greece and Macedonia at a camp near the village of Greek village of Idomeni.
She said 210 people had been allowed to cross from Greece into Macedonia Monday. Meanwhile, UNHCR said the numbers of migrants at Idomeni had swollen to 8,500 Monday night, with 1,500 having spent the previous night in the open. Heavy rains worsened conditions Monday night.
Mohammed Ghareeb, a translator with a Doctors Without Borders (MSF) medical team at Idomeni, described wretched conditions at the camp, where he has worked for more than a year.
There are not enough tents, he told CNN, and women and children often fall ill.
"They are tired from their journey and they don't know why they are here, why they are not allowed through," he said.
Migrant influx in two months similar to first half of 2015
The number of migrants in Greece needing accommodation has soared to 24,000 since restrictions were introduced along the Balkans route, UNHCR said in a statement.
And in the first two months of the year, it continued, more than 131,000 migrants had entered Europe -- a number that was close to the total for the entire first half of 2015.
German Chancellor Angela Merkel said at a news conference in Berlin Tuesday that the European Union needed to stick to its obligation, made in September, to resettle 160,000 refugees among its members over two years. So far, only hundreds have been resettled.
Read: Welcome to the Jungle
She also said European countries needed to reinstate the Schengen system of border-free travel within Europe to deal with the crisis. Many countries have implemented extra border controls in response to the migrant influx.
CNN's Kellie Morgan, Noisette Martel, Stephanie Halasz and Marilia Brocchetto contributed to this report.
