French police on Tuesday dismantled a camp of about 800 migrants in the port city of Calais, the biggest such operation since the sprawling "Jungle" shantytown was broken up four years ago.

Calais continues to attract migrants from the Middle East and Africa who set up makeshift camps along France's northern coast from where they hope to make the passage across the English Channel to Britain.

Since January 1, French authorities have intercepted at least 1,317 migrants as they tried to reach the UK, some by swimming across the busy waterway.

Tuesday's operation started before dawn and had evacuated more than 600 people in 30 buses by the afternoon, according to local authorities, who added that 34 people were detained.

"We want to avoid a concentration and a new gathering point in Calais," Louis Le Franc, the government's top official for the northern Pas-de-Calais department, said at the scene.

According to Le Franc, it was the biggest dismantling of a Calais camp since the Jungle was cleared of some 9,000 migrants between 2015 and 2016.

The Pas-de-Calais prefecture said there were about 500 tents at the site, with conditions posing "serious problems of security, health and tranquility", particularly for staff and patients of a nearby health centre.

The evacuated migrants will be brought to reception centres in Pas-de-Calais, other departments in northern France, and other regions of the country.

'Safe haven' 

By far the majority of the migrants are men, mainly from Somalia, Sudan, Iran, Iraq and Eritrea.

"In my view, this is above all an operation to give people a safe haven. The migrants are living in this forested area in extremely difficult conditions," Le Franc said.

"It was important to get the migrants out before... the winter period," he added.

Northern France has long been a magnet for people seeking to smuggle themselves to Britain in small boats or in one of the tens of thousands of trucks and cars that cross over daily on ferries and trains.

In August, a Sudanese teenager drowned while trying to reach Britain with a friend in an inflatable boat.

French authorities have vowed to avoid a new incarnation of the Jungle — which at one point held as many as 10,000 people — but camps have continued to spring up as migrants flee war and poverty at home to seek a better life in Europe.

Rights groups have criticised police tactics, which include seizing migrants' tents and other belongings.

In December 2018, France's human rights ombudsman said migrants in northern France have been subjected to "unprecedented" violations of their basic rights.

As Tuesday's evacuation was underway, migrants queued for buses grouped by nationality, as tents, duvets, blankets, shoes and clothes were left behind in the undergrowth.

"Our goal is also to fight actively against smugglers" and "the exploitation of human misery", Le Franc said.

Serves 'no purpose' 

Rights associations said the operation was pointless. 

Maya Konforti of the Auberge des Migrants (Migrants' Hostel) group said the evacuated foreigners would be back "within days".

"We spend a lot of money to move dozens of people in buses... but it serves absolutely no purpose. It's messaging, nothing else," she said.

The migrants know that few of them qualify for asylum in France, and believing that "England is their last chance" will continue trying to get there at all costs, Konforti said.

Yolaine Bernard of the Salam association said many had escaped Tuesday's roundup, and will now wander the streets of Calais "without a blanket, without a tent. They no longer have anything, no more clothes". 

The government estimates that about 1,000 migrants live around Calais, while support groups say the number is closer to 1,500.

The Anafe migrant assistance group on Tuesday issued a report denouncing alleged rights violations on France's borders, including officials preventing newcomers from filing asylum claims.