An EU border force has begun arriving in Greece to help stem an influx of illegal migrants - the first such EU team to be deployed.
The EU border agency Frontex says 175 border control specialists are heading for the Orestiada area, near the Greek-Turkish land border.
Many of the illegal migrants claim to be from Afghanistan.
Dozens continued to enter Greece illegally at the weekend, the Associated Press news agency reported.
Up to 300 illegal migrants have been arriving daily, Greek officials say. Last week Greece appealed to Frontex for help.
In the second quarter of this year 90% of the migrants detected trying to enter the EU illegally were on the Greek land border, Frontex says.
Frontex says the Rapid Border Intervention Team's (Rabit's) mission will last up to two months.
The team includes experts on clandestine entry, false documents and stolen vehicles, as well as dog handlers and interpreters.
Romania is providing a helicopter, as well as patrol cars and buses.
Germany, Austria, Bulgaria and Hungary are also providing vehicles and other equipment.
Greece reported a total of 45,000 illegal border crossings for the first half of this year.
The European Commissioner for Home Affairs, Cecilia Malmstroem, said illegal migration was particularly "dramatic" along a 12.5km (eight-mile) stretch near Orestiada.