The number of unaccompanied child migrants living in "dirty" Greek detention centres has increased "alarmingly", a human rights organisation has warned.

An estimated 117 children were in police cells or custody centres in Greece at the end of July, compared to just two in November 2016, according to figures released by the country's government.

Under Greek law, the authorities should separate minors into safe accommodation, where they are appointed guardians who represent them in legal proceedings.

But when there is no space in safe shelters, the authorities detain them in police stations and immigration detention facilities, sometimes with unrelated adults.

“Instead of being cared for, dozens of vulnerable children are locked in dirty, crowded police cells and other detention facilities across Greece, in some cases with unrelated adults,” said Eva Cossé, the country's researcher at Human Rights Watch.

“The Greek government has a duty to end this abusive practice and make sure these vulnerable kids get the care and protection they need.”

Human Rights Watch has written to Migration Policy Minister Yiannis Mouzalas to stop the automatic detention of unaccompanied children.

It suggested the government should amend legislation and significantly shorten the amount of time a child can be detained in protective custody.

Inside the classroom with Chios's child refugees Show all 13 1 /13 Inside the classroom with Chios's child refugees Inside the classroom with Chios's child refugees Inside the classroom with Chios's child refugees Volunteers walk a group of refugee children towards their school on the island of Chios AFP/Getty Inside the classroom with Chios's child refugees Inside the classroom with Chios's child refugees Refugee children pose at a makeshift camp on the island of Chios AFP/Getty Inside the classroom with Chios's child refugees Inside the classroom with Chios's child refugees A Syrian Kurd mother combs Roza's hair, as she prepares to go to a volunteer-run school in a refugee camp on the island of Chios AFP/Getty Inside the classroom with Chios's child refugees Inside the classroom with Chios's child refugees Refugee children attend an English language class at the volunteer run school on the island of Chios AFP/Getty Inside the classroom with Chios's child refugees Inside the classroom with Chios's child refugees Refugee children carry vegetables in a refugee camp on the island of Chios AFP/Getty Inside the classroom with Chios's child refugees Inside the classroom with Chios's child refugees A newly arrived Syrian refugee, 13, holds her sister, 2, in a makeshift camp on the island of Chios AFP/Getty Inside the classroom with Chios's child refugees Inside the classroom with Chios's child refugees Refugee children pretend they go to school as they play in a refugee camp in the island AFP/Getty Inside the classroom with Chios's child refugees Inside the classroom with Chios's child refugees A Greek girl walks past a graffiti on her way to a school on the island of Chios AFP/Getty Inside the classroom with Chios's child refugees Inside the classroom with Chios's child refugees A Malian refugee child poses from behind a fence in a makeshift camp AFP/Getty Inside the classroom with Chios's child refugees Inside the classroom with Chios's child refugees A Syrian Kurd mother combs Roza's hair, as she prepares to go to a volunteer-run school in a refugee camp on the island of Chios AFP/Getty Inside the classroom with Chios's child refugees Inside the classroom with Chios's child refugees A Syrian family from Aleppo newly arrived to Greece sits in a makeshift camp on the island of Chios AFP/Getty Inside the classroom with Chios's child refugees Inside the classroom with Chios's child refugees A child carries a broken blackgammon game in a makeshift camp on the island of Chios AFP/Getty Inside the classroom with Chios's child refugees Inside the classroom with Chios's child refugees A child holds onto her mother, Djeneba from Mali, before attending school in a refugee camp on the island of Chios AFP/Getty

While they wait for a space in a shelter, many children are not provided with information about their rights and are not told how to apply for asylum, the organisation said.

Aid workers have previously reported that the uncertainty and distress caused by the asylum process, exacerbated an ongoing mental health crisis among migrants living on the islands.

Children as young as nine have harmed themselves, while 12-year-olds have attempted to kill themselves, Save the Children said in March.