See: Crossing a Red Line: How EU Countries Undermine the Right to Liberty by Expanding the Use of Detention of Asylum Seekers upon Entry (ECRE, link):
““Crossing a Red Line” explains that while there has been a significant decrease in asylum applications in Bulgaria, Hungary and Italy, the use of detention upon entry has been increasing since 2015 and continues to do so. Practises of de facto detention- which indicates the deprivation of an individual’s liberty without the requirement of a detention order- are widespread and specific to country context. Hot spots, transit zones, pre- removal centres, border zones at which migrants have been ‘pushed- back’ and boats- including search and rescue vessels- have all become spaces in which people can be detained. In other cases “protective detention” results in unaccompanied children having their freedom of movement restricted.
With no procedural guarantees and no opportunity to seek judicial review, the only possibility for release from de facto detention is to leave to another country.”