Officers stopped mostly African and Asian people in the street for identification checks. Most were only briefly detained, but about 1,600 were arrested for illegal entry and sent to holding centres pending deportation.

Some 100,000 illegal immigrants are estimated to slip into Greece every year and up to a million are believed to live in Greece, which has an official population of about 10 million.

The Public Order Minister, Nikos Dendias, said their unchecked entry brought Greece "to the brink of collapse".

"The country is being lost," he said. "What is happening now is [Greece's] greatest invasion ever. Since the Dorian invasion some 3,000 years ago, the country has never received such a flow of immigration."