Greece has asked for extra European help to patrol its border with Turkey.
Greece is now the main entry point into Europe for illegal immigrants, and the government in Athens says it can't cope with the influx.
The European Commission has promised immediate assistance. It is sending border guards to help Greece stem an influx of migrants entering across the land border with Turkey.
Many of the illegal migrants claim to be from Afghanistan.
The commission said the flows of illegal migrants entering Greece have "reached alarming proportions".
The Frontex border agency says that overall, there is a clear decline in the numbers of illegal migrants seeking to enter the EU.
But it reports that illegal crossings on Greece's land border with Turkey have intensified.
It recorded a six-fold increase there in the number of Afghans trying to enter Greece in the second quarter of this year.
In total during that period, 90% of the migrants detected trying to enter the EU illegally were on the Greek land border.
Half of those detected were Albanian workers looking for seasonal jobs in Greece, Frontex says. Albania borders on northwestern Greece.
But the other half - 9,500 - were migrants intent on travelling through Greece to settle in other EU member states.
45,000 incidents in six months
Greece reported a total of 45,000 illegal border crossings for the first half of this year.
European Home Affairs Commissioner Cecilia Malmstroem said illegal migration was particularly "dramatic" along a 12.5km stretch near the Greek town of Orestiada.
Greek officials quoted by Frontex say up to 350 migrants are trying to enter Greece daily in the Orestiada area.
On 1 October, Frontex opened a regional centre in Piraeus, Greece - it is the agency's first such office outside its headquarters in Warsaw.
The new EU border teams will act as officers of the national border guards They are "authorised to carry their service weapons and wear their own uniform".