Greece has announced plans to close its three largest migrant camps and replace them with facilities on the mainland that campaigners have likened to detention centres.

People living in overcrowded camps on the islands of Lesbos, Chios and Samos will be moved to closed complexes for identification, relocation and deportation with a capacity of at least 5,000 people each.

More than 27,000 people are currently housed on the three islands – which have a nominal capacity of just 4,500 – under conditions that have been repeatedly castigated by rights groups and the Council of Europe.

“Decongesting the islands is a priority at this stage,” said Alkiviadis Stefanis, Greece’s deputy defence minister.

Smaller camps on the islands of Kos and Leros will be remodelled along similar lines and enlarged, Stefanis added. The changes come with winter approaching and hundreds of families sleeping in tents outside official facilities on the five islands.

Asylum seekers will not be allowed to move freely in and out of the camps, said officials, but will instead be locked up until they are either granted refugee status and relocated to the mainland or rejected and sent back to Turkey.

The government has vowed to relocate 20,000 asylum-seekers to camps on the mainland by early 2020.

The new conservative government, which came to power in July, has already passed a law stiffening asylum requirements for migrants, and has pledged to deploy additional border patrols.

Stefanis said the operations of NGO groups that assist migrants would be subject to new criteria.

“Only those (NGOs) that meet the requirements will stay and continue to operate in the country,” said Stefanis.

Kyriakos Mitsotakis, the Greek prime minister, this week accused the EU of treating countries on the bloc’s external frontiers as convenient places to park migrants.

“It cannot go on like this,” Mitsotakis told the German newspaper Handelsblatt.

“Europe regards arrival countries such as Greece as a convenient parking spot for refugees and migrants. Is that European solidarity? No. I will no longer accept this.”

The International Organization for Migration last month said that Greece’s mainland camps are already nearly full or past capacity.