Over 500 undocumented migrants detained for the past three months at the Komotini police academy in eastern Greece have rioted and set fire to the premises.

"The riots have stopped. It is not the first but it is the largest. It is inhumane," a ranking officer told Euobserver on Saturday (November 24) evening.

The entire site is on lockdown.

Outside the gates, a police officer in riot gear stands guard armed with a machine gun in near complete silence. Behind him, a parking lot and the nearby buildings are obscured in darkness. The lights turned off.

The officer says all 520 migrants set fire to their mattresses on Thursday with riots raging all through Friday and into early Saturday. "We don’t know what to do, we do not have a solution," he says.

Four of the 15 guards overseeing the detainees were injured. Another four migrants were reportedly injured and around 50 arrested. Some were chanting "freedom" and "send us home" report local media.

Guards fired tear gas as the migrants, mostly young men from Pakistan and Afghanistan, pelted the officers with rocks.

The scale of the violence has prompted Greece's minister of public order to hold a late night meeting with the city's public authorities.

The young men at Komotini were swept up from Athens as part of Greece's operation "Xenios Zeus." Prime Minister Antonis Samaras had launched the campaign in the beginning of August in an effort to "clean up" and "make safe" Athens.

The campaign's first week detained in Athens some 6,030 people suspected of having entered the country illegally. Greek police then arrested 1,525 of them.

"Those arrested will be deported to their home countries," a spokesperson for Greece’s ministry of public order and citizen protection told this website in an email in August.

Authorities says Xenios Zeus will spread throughout the entire country.

But housing the migrants rounded up en masse has posed a number of logistical problems. Authorities are placing them in residences once used by police cadets, prompting protests from locals who oppose their presence.

Around 1,000 cadets are normally schooled at Komotini's police academy. Now, around 300 remain on site in two of the five buildings. The remaining three buildings have been turned into detention centres.

Residents in surrounding villages say they feel overwhelmed by the number of undocumented migrants that have entered the country.

"Three months ago around a hundred would gather at the train station on a daily basis. Some would ask for food and water and we would give it to them," a farmer at the Nea Vissa border town told this website. "They were very polite and never caused any harm," he said.

But public anti-immigrant sentiment runs high and many favour the 12.5 km razor-wire fence that runs across the land where the Evros river loops into Turkey.

The fence is meant to dissuade people from crossing into the country and forces some to attempt the more perilous river crossing.

A section runs across garlic and asparagus crops that belong to local Nea Vissa farmers. Tractors till the fields up to the fence amid heavy guard from Greek border police, the Greek military, and the EU's border control agency, Frontex.

"In July 2012 we had 6,500 illegal migrants who passed the border. In August, we had only 1,800. In September, only 71 illegal migrants, in October only 26 and now there are none," said Pashalis Syritoudis, chief of police at Orestiadas on the Greek Turkish border.

Meanwhile, border police continue to stop vehicles at random along the E85 highway that runs the length of the border.

Four police patrol points are set up between the 120 km stretch of highway between Orestiadas in the north and Alexandroupoli in the south. The officers are checking vehicles for smuggled migrants.

Locals at a village in Peplos in the Evros Delta told EUobsever that smugglers avoid the highway. "They take the back roads and villages and go through the mountains," they said.