The Greek government has been criticised after announcing it will build a floating barrier to deter thousands of people from making often perilous sea journeys from Turkey to Aegean islands on Europe’s periphery.

The centre-right administration unveiled the measure on Thursday, following its pledge to take a tougher stance on undocumented migrants accessing the country.

The 2.7km-long netted barrier will be erected off Lesbos, the island that shot to prominence at the height of the Syrian civil war when close to a million Europe-bound refugees landed on its beaches. The bulwark will rise from pylons 50 metres above water and will be equipped with flashing lights to demarcate Greece’s sea borders.

Greece’s defence minister, Nikos Panagiotopoulos, told Skai radio: “In Evros, natural barriers had relative [good] results in containing flows,” referring to the barbed-wire topped fence that Greece built along its northern land border with Turkey in 2012 to deter asylum seekers. “We believe a similar result can be had with these floating barriers. We are trying to find solutions to reduce flows.”

Amnesty International slammed the plan, warning it would enhance the dangers asylum-seekers and refugees encountered as they attempted to seek safety.

“This proposal marks an alarming escalation in the Greek government’s ongoing efforts to make it as difficult as possible for asylum-seekers and refugees to arrive on its shores,” said Massimo Moratti, the group’s Research Director for Europe.“The plan raises serious issues about rescuers’ ability to continue providing life-saving assistance to people attempting the dangerous sea crossing to Lesbos. The government must urgently clarify the operational details and necessary safeguards to ensure that this system does not cost further lives.”

Greece’s former migration minister, Dimitris Vitsas, described the barrier as a “stupid idea” that was bound to be ineffective. “The idea that a fence of this length is going to work is totally stupid,” he said. “It’s not going to stop anybody making the journey.”

Greece has seen more arrivals of refugees and migrants than any other part of Europe over the past year, as human traffickers along Turkey’s western coast target its outlying Aegean isles with renewed vigour. More than 44,000 people are in camps on the outposts designed to hold no more than 5,400 people. Human rights groups have described conditions in the facilities as deplorable. In Moria, the main reception centre on Lesbos, about 140 sick children are among an estimated 19,000 men, women and children crammed into vastly overcrowded tents and containers.

Amid mounting tensions with Turkey over energy resources in the Mediterranean, Greece fears a further surge in arrivals in the spring despite numbers dropping radically since the EU struck a landmark accord with Ankara to curb the flows in March 2016.

The prime minister, Kyriakos Mitsotakis, who trounced his predecessor, Alexis Tsipras, in July partly on the promise to bolster the country’s borders, has accused the Turkish president, Recep Tayyip Erdoğan, of exploiting the refugee drama as political leverage both in dealings with Athens and the EU. As host to some 4 million displaced Syrians, Turkey has more refugees than anywhere else in the world, with Erdoğan facing mounting domestic pressure over the issue.

Greek officials, who are also confronting growing outrage from local communities on Aegean islands, fear that the number of arrivals will rise further if, as looks likely, Idlib, Syria’s last opposition holdout falls. The area has come under renewed attack from regime forces in recent days.

It is hoped the barrier will be in place by the end of April after an invitation by the Greek defence ministry for private contractors to submit offers.

The project is expected to cost €500,000 (£421,000). Officials said it will be built by the military, which has also played a role in erecting camps across Greece, but with “non-military specifications” to ensure international maritime standards. The fence could extend 13 to 15km, with more parts being added if the initial pilot is deemed successful.

“There will be a test run probably on land first for technological reasons,” said one official.