French authorities have bulldozed three makeshift migrant camps that had been sheltering hundreds of refugees at the port of Calais, citing health concerns following an outbreak of scabies and increasing violence.

The authorities claimed the areas needed clearing because of "deplorable hygiene" conditions.

There were also complaints from local people and officials that the number of migrants in the port area and "at the mercy of people smugglers" offering to take them to Britain had doubled in the past few weeks.

However, there was no indication of where the hundreds of migrants, many of whom have fled conflicts in Syria and Afghanistan, could or would go.

The French authorities had organised a fleet of buses to take the migrants to a centre where they could shower and be given new clothes, but most refused fearing they would be taken far from Calais.

Aid organisations said dozens of migrants, warned of the impending police operation, had made last-ditch attempts to cross the Channel. Border police reported groups of 30 to 40 people hiding in shrubs along roads leading into the port. Some were attempting to jump on lorries as they slowed down.

A young Sudanese migrant was killed on Friday after trying to conceal himself near the axle of a coach that had stopped in a supermarket car park.

"As if the situation isn't tragic enough, it is intolerable that once again these expulsions are being carried out without any alternative being proposed," said Jean-Claude Lenoir, president of Salam, which has been offering meals to the migrants.

Humanitarian organisations distributed tents to some of the migrants and lambasted the authorities for "a show operation that solves nothing". In a letter to the prime minister, Manuel Valls, and other ministers 10 humanitarian groups, including Médecins du Monde (MDM)and the Secours Catholique, attacked the authorities for failing to address the Calais camp problem.

"The situation in Calais is deteriorating in a deafening silence. Despite having repeatedly warned the public powers of the threat to public health that this situation is causing, no proper response has yet been proposed," they wrote.

Jean-François Corty, of MDM, said it was impossible to treat the scabies outbreak and at the same time dismantle the camps, leaving the affected migrants with nowhere to go.

"I am scandalised and furious," he told journalists at the scene, adding that the forced evacuation, like previous operations, would change nothing.

"They evacuate and everything starts over again. A few months, years after the evacuation, everything is the same," he said.

The clearing of the camps came just days after France's anti-immigration Front National won the north-west constituency in the European elections. FN president Marine Le Pen, who stood for election in the region, scored 34% of the vote, tripling the party's 2009 European election score.

Between 800 and 850 migrants were believed to be in the Calais area, while up to 650 were in the city's port area hoping to reach Britain. The notorious camp at Sangatte known as the "jungle", which held up to 2,000 refugees all hoping to cross the Channel, was closed in a joint agreement between Britain and France in 2002.

After meeting humanitarian organisation leaders last week the Calais prefect, Denis Robin, told journalists that migrants who were minors or considered the "most fragile" would be helped.

However, he said the camps were a health risk and centres of violence and could not be allowed to remain.

"Given the larger and larger concentration of squats in the public port area, given the increasing violence between the [smugglers'] networks and the health problems, we have no choice but to act in the interest of public order," he told French television.

The French interior ministry said minors would be offered shelter while adult migrants would be found temporary accommodation outside the Calais area.

Jalal, an Iraqi refugee in his early 20s, watched his camp being dismantled from a distance.

"It's sad and it changes nothing. I'll pitch my tent elsewhere. I'm going to hide and not be with the others. We'll be less safe and we'll have to hide, but I'm staying here," Jalal told Reuters.

"I'm going to try to cross [to England] again. I've not come all this way here to give up now."