It's nightfall in Poros, a small village in northeastern Greece. Tractors lie idle and the streets virtually deserted.

Tranquil the site may look but it has become a favoured entry point for migrants, as locals know only too well, prompting some to join so-called citizens patrols.

Despite the late hour, farm worker Sakis, clad in military fatigues, is wide awake, as he patrols along the river Evros, right on the Turkish border, his goal "to defend the gates of Greece and of Europe."

The border between EU member Greece and non-member Turkey has become a major flashpoint once again since Turkish President Recep Tayyip Erdogan gave migrants the green light to leave for Europe last week.

The river Evros, which forms a natural border between Greece and Turkey, is once again a migrant flashpoint for the two neighbours
The river Evros, which forms a natural border between Greece and Turkey, is once again a migrant flashpoint for the two neighbours AFP / Sakis MITROLIDIS

The move sparked fears of a repeat of the migrant crisis of four years ago, when more than one million people crossed into the EU, and Greeks near the border have responded with patrols.

Some consist of well-equipped police. But others comprise in their ranks agricultural workers, hunters, fishermen and breeders determined to block access.

Sakis, 38, explains that the idea is to "avoid an invasion" as he heads off to check out his sector, hunting rifle slung over his shoulder, eschewing sleep and growing exhaustion.

"Day and night I do the rounds in my car along the river path to see if boats are trying to make it to the Greek side".

As soon as migrants are spotted, police or the army are tipped off to deal with them.

Despite Greece stepping up border patrols, migrants eye up their chances of making it across the river running along the border
Despite Greece stepping up border patrols, migrants eye up their chances of making it across the river running along the border AFP / Ozan KOSE

Giokas Xanthos relies on his knowledge of the riverbank as a keen fisherman to target areas where traffickers might be aiding migrants to cross.

"We know the terrain like the back of our hand and that can be useful for the authorities," he says.

With the 2015 influx still fresh in the memory, it is easy to lapse into xenophobic language as they try to seal the border.

"With Turkey as a neighbour we live with a permanent threat. We need concrete help from Europe and not just promises," says Poros's mayor, Athanassios Pemoussis, who called on local people to "support Greek forces of law and order in a difficult struggle."

Erdogan's move came after Russian-backed Syrian forces killed 34 Turkish troops in northern Syria, prompting him to seek greater assistance from the international community.

Greek soldiers -- but also armed citizen groups -- patrol the banks of the river on the border as migrant ranks swell once again
Greek soldiers -- but also armed citizen groups -- patrol the banks of the river on the border as migrant ranks swell once again AFP / Ozan KOSE

That has persuaded tens of thousands of people to try their luck reaching Greece. Recent days have seen scuffles near the Pazarkule-Kastanies border post as migrants look to stream in from Turkey.

The owner of the "Jojo Wild Rose" cafe on the Greek side says there are no militia groups in his sector "as, with the barbed wire here, the migrants can't pass."

But, slightly further south, as migrants probe for potential points of entry along an often porous border stretching for 212 kilometres (70 miles), he volunteers that there are patrols "made up of soldiers who have been retired for some years."

Since Tuesday, Dimitris Kolgionis, deputy mayor of Pheres, a commune of some 5,000 people which includes Poros, has been organising border patrols.

"Five hundred people answered the call and are working in shifts," he said.

From 9:00 am to 1:00 pm on Wednesday it was the turn of Giorgos Ioumis, a pensioner, to join the citizen patrol.

"The whole Evros region has mobilised. We are in a war zone and we have to defend our territory," he insisted.

Kizialidis Kizialis, a 60-year-old Poros farmworker, admits he is "afraid of migrants" while saluting the efforts of the government and the police.

Getting through the net at Poros looks nigh on impossible now that Athens has doubled patrols there and along all of its land and sea borders while urging EU border agency Frontex to provide reinforcements.

The Greek government says some 7,000 attempts at illegal entry were stopped in 24 hours between Wednesday and Thursday morning, while 24 arrests were made as mainly Afghan and Pakistani migrants tried to make it across.

On Monday, some 20 tractors fitted out with powerful search lights lined up along the border to floodlight the vicinity in a bid to distract any would-be attempts.

"A show of force which has proved effective as several people were arrested," says Poros mayor Pemoussis.

Greek media have also reported arrests by groups of armed citizens.

"We are armed for protection," says Sakis. "We are determined to guard our borders. And if an accident should occur, it will!"