A 50-strong mob of frustrated young men threw missiles at the officers who responded with tear gas and baton charges.
The unrest comes 36 hours before the sprawling shanty town close to the Calais ferry port is cleared.
French authorities have announced they will clear all migrants out of Calais and destroy the 'Jungle' camp, starting Monday.
The trouble at the camp comes as more than 50 girls arrived at the Lunar House immigration centre in Croydon, south London, on Saturday night.
The group of 54 girls are the first child refugees to enter the UK from Calais under the Dubs amendment - a government pledge to help minors, reports The Observer.
The newspaper reports that the girls, most of whom are from Eritrea in Africa, were brought to the UK under the amendment - which could spark an increase in the number of young migrants coming to Britain.
Meanwhile, migrants have been encouraged to claim asylum in France. They will be processed in a nearby warehouse and sent to reception centre across the countries.
Those who refuse to claim asylum and stay in northern France risk arrest and deportation.
The police operation involving some 1,250 CRS riot police is expected to last five days.
The trouble comes after it was revealed that migrants were set to spill out into Northern France in the wake of the planned demolition of the camp.
Unofficial migrant camps without running water and toilets are expected to swell around the area after the Jungle camp is ripped to the ground next week, according to British aid volunteers.
Bulldozers will move in on the slum, with the French authorities saying the estimated 6,500 migrants camped there will be relocated, but some have already started moving on.
Care4Calais founder Clare Moseley said that following the part-dismantlement of the Jungle in February, serious failings were reported at some of the centres migrants were sent to.
She said there was a lack of basic essentials, including access to interpreters and legal advice. And she added: 'We are also concerned that unofficial camps in the north of France will now grow.
'These suffer from a severe lack of infrastructure, no running water, toilets or medical facilities, and so where possible we will also direct aid to these areas.'
Meanwhile, Lily Caprani, UNICEF UK's Deputy Executive Director, has urged the authorities to learn lessons from the last attempted demolition.
'Once the demolition starts there are no second chances,' she said.
'If it results in a single child going missing, or forces them into the hands of smugglers and traffickers, then we will have failed them
'The authorities must prove they have learnt the lessons from last time and keep every child safe throughout this process.
'During the last demolition, which saw people scattered by tear gas and rubber bullets, more than 100 children went missing because it began before their safety was guaranteed.
'We've seen the Home Secretary achieve real progress by bringing some of the vulnerable children to the UK, but there are hundreds more in Calais still waiting to reach safety.
'The UK has made a commitment to bring these children here, and the demolition doesn't change that.
'This is not the end of the story and it's essential that the UK and French authorities continue to work together to ensure the long-term welfare of every child.'
As France gears up for next year's presidential election, French president Francois Hollande has appeared keen to adopt a firmer stance and finally close the camp.
It has become a symbol of his government's failure to tackle Europe's migrant crisis and a target of criticism from conservative and far-right rivals seeking to unseat him.
Amid reports that migrants may attempt last-ditch bids to cross the English Channel, Kent Police has said it is braced for any fall-out from the demolition.
The force has said it is 'monitoring events' in northern France as notices started to go up in the camp alerting migrants to the imminent clearance.
Meanwhile in Kent, a 'White Lives Matter' march is planned on Saturday in Margate. A counter-protest by anti-racist locals has also been organised.