Rioting broke out among teenagers on the site of the largely cleared Calais camp, hours before they were due to be taken from the site in buses to undisclosed locations around France.

About 20 police riot vans arrived early on Tuesday evening and teargas was used to quell fighting and protests among the remaining estimated 1,500 asylum seekers, most of whom are teenagers.

The violence came at the end of a day of mounting tension after minors were told that they were to be removed to “juvenile centres” across France on Wednesday morning. Those with family in the UK, or who have specific vulnerabilities that may make them eligible to claim asylum in the UK, were told that their applications would be processed from the new locations.

The Calais prefecture issued a notice in nine languages informing the people still living in disused shipping containers on the site of the now-demolished camp that they needed to register for wristbands, securing them a place on the buses which will begin leaving at 8am.

A riot policeman patrols close to where 1,500 minors are being housed in converted shipping containers. Photograph: Pascal Rossignol/Reuters

British officials would be on the buses, accompanying the asylum-seeking children, the notice added. “No further applications for transfer to the United Kingdom will be dealt with in Calais,” the statement read. “All cases will be handled and all departures for the UK will take place from the juvenile centres.”

The absence of any detail about the destination of the buses caused great anxiety among the child refugees. By the fenced-off container area of the site, there were hundreds of people milling around, most of whom were very confused about what was planned.

Aladdin Adam, 16, from Sudan, had been given a wristband marked 33 and had been told to be ready at 8am. “I am so worried. I don’t know where I will be going. Everyone is feeling worried; some people are feeling angry,” he said.

That anger erupted into protests as dusk fell and large groups of teenage migrants made their way from the shipping containers into the deserted camp, carrying sticks and shouting. Some vehicles’ windows were smashed and some asylum seekers were reported to have been injured.

Among the remaining camp population there were a smaller number of 11 or 12-year-olds but the majority seemed to be slightly older teenagers, perhaps aged between 15 and 17. There were a few visibly older people claiming to be minors, who appeared to be leading the protests.

There was anger from volunteers, who have worked with the younger Calais residents for the past year, that the children had been left behind after the adult population was taken last week to accommodation around France.

Michael McHugh, who worked with unaccompanied child refugees, said he was dismayed to find more riot police on site than social workers, teachers or therapists. “These are some of the most vulnerable children in Europe,” he said.

Tina Brocklebank, from Help Refugees, said: “If it had been up to us we would have got the most vulnerable children out first. They are completely at risk and vulnerable.”

This final large-scale transfer may be the last major stage of the Calais camp clearances. Throughout the day trucks were taking away debris from the camp, crushing tents and wooden shacks, and the grinding noise of bulldozers was audible throughout the camp.

An aerial view of earthmoving equipment at work on the site of the Calais camp on Tuesday. Photograph: Philippe Huguen/AFP/Getty Images

Wasil Anwari, 14, who said he fled Afghanistan earlier this year after both his parents were killed, showed a purple wristband marked Bus 30. He said he had been given no information about where in France they were going to be taken. He was hoping to be given papers allowing him to come to the UK eventually, so that he could join his uncle, who works in a shop in London.

Some people thought that the buses were going to take them straight to London; others thought they would be driven to Lille. “We aren’t given a choice. We will go somewhere in France, but we don’t know where,” Wasil said.

Noorullah Hussaini, 17, from Afghanistan, also had a purple wristband and was preparing to leave on a bus on Wednesday. He said he hoped that his application to join his sister in Manchester would eventually be successful, after a 30-minute interview with Home Office officials in the camp last week.

“They told me it would take between two weeks and two months,” he said. He said he hoped to study to become a dentist in the UK. Because he was confident that his request would be granted, he said he was not trying to come illegally to the UK on the back of lorries. But several other young people said they were continuing the night-time attempts to head to England by smuggling themselves into vehicles, convinced that this was the best option for them to rejoin family in the UK.

“I want to go legally. There are too many dangers on the lorries,” Noorullah said.

Children were carrying belongings in plastic bin bags, many of them wearing flip-flops and shorts in the November weather.

The cleanup continued around them, as workers gathered abandoned duvets hanging in the trees, half-burnt tents and singed blankets submerged in the sand.

Digena Gesesew, 17, from Ethiopia, was with friends, washing some clothes in a bucket and hanging them on the fencing to dry. “The bus will leave at 8 tomorrow morning. I don’t know where we will go,” he said. “It’s very difficult.”

The French authorities declared the cleanup complete on Monday, but at the edges of the camp small clusters of tent remained, with people living in them. The president, François Hollande, said on Tuesday that an increased police presence around the camp would ensure that people were not able to return. But there were new arrivals, some from an informal migrant camp in Paris, who had come to see if they could find space on a coach to London.

Ben Teuten, the co-founder of Refugee Youth Service, a charity that has looked after minors in the camp for the past year, said he was disappointed by the lack of clear information for young people. “All the decisions have been quite poorly communicated. The children are very confused and scared. The children are left not knowing what their status is. We have a real concern that many have been given false hope when we know a lot of them won’t be going to the UK.”

He said he was worried that a lot of the children would disappear from the French children’s centres once it became clear that there was little prospect of them being transferred legally to the UK.