More than 300 refugee children have disappeared in Sweden in the first four and a half months of the year, according to the most recent figures.

Last year, 420 minors who arrived in Sweden without their parents left their asylum homes without reporting their departure to authorities, according to Stockholm’s county administration board.

The authority was appointed by the government to examine why, and how many, young refugees disappear after they are registered in the system as seeking asylum in Sweden.

And officials raised concerns on Thursday about the rising number of disappearances in 2016, which is already well on its way to breaking last year’s record. A total of 313 are currently missing, according to the Svenska Dagbladet (SvD) newspaper.

“How will you find food? How will you get money? For an adult to give you money they might demand a quid pro quo, such as sexual services or committing crimes,” Kjell-Terje Torvik, who works with children for the Swedish Migration Agency (Migrationsverket), told SvD.

While some choose to return to their home countries, he said it was often difficult to say why the minors leave their temporary accommodation in Sweden, adding that it varies depending on their stage in the asylum application process.

“If the disappearance comes after a decision, it is often triggered by an asylum rejection, but if it happens before a decision it is not as certain what triggered it,” said Torvik, who claims that many of the unaccompanied refugee children end up on the street, often falling victim to prostitution or crime.

“The number is concerning, but it is also not clear because you don’t know the reason for their disappearance. But of course there is a risk that prostitution would rise when the children have no money, no structures and nowhere to live,” police officer Christian Frödén told the newspaper.

Sweden took in a record 163,000 asylum seekers fleeing wars in Africa and the Middle East in 2015, including more than 35,000 unaccompanied minors, two thirds of whom came from Afghanistan.

Migration authorities have previously said they expect a surge in the number of asylum seekers going underground in the next three years, estimating the number at as many as 46,000, including adults.

In October last year officials in Trelleborg in southern Sweden told The Local that they believed almost 1,000 unaccompanied refugee children and young adults had gone missing before even having their paperwork processed by the Migration Agency.