The European Commission is demanding restraint following clashes between Greek island residents and riot police over plans to build new migrant-detention camps.

"As in all cases we would expect the member state authorities to address such situations using measures that are necessary and proportionate," a European Commission spokesperson told reporters in Brussels on Tuesday (25 February).

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The comment follows the eruption of riots on the Greek islands of Lesbos and Chios by residents who oppose plans to build the new centres.

Greek media report some 200 riot police have been sent in to quell the unrest, following demands by locals to have the centres built on the mainland instead.

The commission says such measures are not financed by itself nor by European funds, adding that island security is a prerogative of national authorities.

Thousands of migrants and people seeking international protection remain trapped in overcrowded, violent, and open camps.

Those camps are part of the so-called 'hotspot' concept developed by the European Commission in 2015, which it praised as a success late last year.

'Shocking and shameful'

Among the largest is Moria on Lesbos. It is designed to house some 3,000 people - but is home to almost 20,000.

Dimitra Kalogeropoulou, who is the Greece director for the International Rescue Committee, said such tensions come as no surprise.

"Local communities have been impacted by the government's policies towards asylum seekers, especially the containment policy, which has trapped over 40,000 people on the islands," she pointed out.

Some have spent more than two years in the Moria alone, often living in shared tents and in conditions that have shamed both Greece and the European Union.

In a statement over the weekend, Filippo Grandi, UN High Commissioner for Refugees, had also described the conditions on the islands as "shocking and shameful."

"The risks faced by the most vulnerable individuals - pregnant women, new mothers, the elderly and children - are among the worst seen in refugee crises around the world," he said.

Such hotspots appeared after Greece closed down its land border with Turkey along the Evros river, given a sudden large inflow of people at the time.

Part of that containment effort included a 12.5-km-long fence along a stretch of river that loops into Turkey. Watchtowers had also been erected and equipped with 23 thermal vision cameras, co-funded by the EU.

The hotspots concept was also dovetailed into the EU agreement with Turkey in early 2016, which aimed to prevent people from arriving on the islands from Turkey in exchange for billions in aid to Ankara and other political concessions.

Turkey has been using the agreement as leverage to draw concessions over a European Union that seeks to prevent a repeat of 2015 when some one million people arrived demanding asylum.

But people are still arriving. Almost 60,000 arrived by sea last year alone.

Greece is now mulling plans to create a 2.7km floating net barrier between the Greek and Turkish coastline.