IDOMENI, Greece (AP) — Macedonian special police forces fired stun grenades Friday to disperse thousands of migrants stuck on a no-man?s land with Greece, a day after declaring a state of emergency on its borders to deal with a massive influx of migrants heading north to the European Union.

The crowd of 3,000 migrants who spent night out in the open made several attempts Friday to charge Macedonian police after the border was shut to crossings the previous day. At least eight people were injured in the melee, according to Greek police. One youngster was bleeding from what appeared to be shrapnel from the stun grenades that were fired directly into the crowd.

Police backed by armored vehicles spread coils of razor wire over rail tracks used by migrants to cross on foot from Greece to Macedonia.

Greece has seen an unprecedented wave of migrants this year, the vast majority fleeing war and conflict in Syria and Afghanistan, crossing clandestinely to its islands from the nearby Turkish coast, with more than 160,000 arriving so far. The influx has overwhelmed Greek authorities, particularly on the islands, many of which are small tourist destinations unequipped to deal with mass arrivals of refugees.

Few, if any, of the migrants arriving want to remain in Greece, a country in the grip of a financial crisis. The vast majority head straight to the country's northern border with Macedonia, from where they cram onto trains and head north through Serbia and Hungary on their way to the more prosperous European north and countries such Germany, the Netherlands and those in Scandinavia.

Macedonian police spokesman Ivo Kotevski said Thursday that both police and the army would control the 50-kilometer (30 mile) border stretch to stop a "massive" influx of migrants coming from Greece.

"This measure is being introduced for the security of citizens who live in the border areas and for better treatment of the migrants," he said.

Until now, the border has been porous, with only a few patrols on each side. Sealing it disrupts the Balkan corridor for migrants who start in Turkey, take boats to Greece or walk to Bulgaria, then make their way through Macedonia or Serbia heading north to the EU.

Almost 39,000 migrants, most of them Syrians, have registered as passing through Macedonia over the past month, double the number from the month before.

And hundreds arrive each day on Greek islands. The Greek coast guard said Friday it had picked up 620 people in 15 search-and-rescue operations in the last 24 hours off the islands of Lesbos, Samos, Agathonissi, Leros, Farmakonissi, Kos and Megisti. That doesn't include the hundreds more migrants who manage to make their own way to the islands in inflatable dinghies.

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Elena Becatoros in Athens contributed