The number of missing child refugees in Germany has doubled since the start of the year with almost 9,000 believed to have disappeared.
Germany's federal police confirmed on Monday that 8,991 unaccompanied refugee children had been reported missing as of July 1, already higher than the whole of last year. Most of those who have disappeared are teenagers but 867 are under 13 years old.
The German police unit Bundeskriminalamt (BKA) insisted the increase could be down to young people registering in more than one authority. A spokesman said it was hard to keep a record as many arrived with no identification and spelt their names in different ways.
"In many cases, it's not like the children left without a plan," he added. "They wanted to visit their parents, relatives or friends in other German cities or even other European countries."
But charities expressed concern the children could be forced into crime or trafficked into forced labour or prostitution.
A spokesman for Save the Children said the charity was "extremely worried" by the figures.
"Unaccompanied children are fleeing conflict and making treacherous journeys to reach safety in Europe, only to fall through the cracks in the European system," a spokesman for the charity said.
"There are a lot of different reasons why refugee children in Europe are failing to be accounted for. Many have not been properly identified and registered, many abscond from the facility centres they are placed in, choosing instead to make the journey on their own. These children are at high risk of becoming victims of exploitation, trafficking and other forms of abuse."
The figures are likely to increase pressure on the UK to allow more unaccompanied children in Europe to enter the UK.
Tim Farron, Liberal Democrat leader and evangelical Christian, has campaigned alongside Save the Children for Britain to take its "fair share" of child refugees.
"I've been to the camps, I've seen families absolutely devastated, people who've fled war and persecution, the threat of death for them and their children and they took an enormously risky decision to cross the water to come to Europe. Why? Because what they left behind was riskier still," he told the BBC.
The figures in the German newspaper Neue Osnabrücker Zeitung came as about 6,500 migrants were rescued in one day off the Libyan coast. The Italian coastguard described Monday's mission as one of its biggest operations to date. A further 1,100 were rescued in the same area on Sunday.
