Hundreds of migrants from a camp in Diavata near Thessaloniki have spent Thursday night in the open hoping to flee via North Macedonia to Europe.
Earlier, dozens clashed with the Greek riot police after trying to break through a cordon. They threw stones at police who responded with tear gas and stun grenades.
No injuries or arrests were reported.
In the wake of anonymous calls on social media for a long trek through heavily guarded Balkan borders, police said more than 500 people, including families with small children, assembled in a cornfield outside the Diavata migrant camp, which is around 10 kilometers (6 miles) west of the city of Thessaloniki.
Some set up tents as dozens more approached on foot.
Migrants, most of whom have already requested asylum in Greece, said they planned to go to the fenced-off border with North Macedonia 60 kilometers (38 miles) away and try to push through. In early 2016, a similar route was firmly shut down after more than a million people flowed through Greece and the Balkans to Germany and other countries.
The United Nations refugee agency has denounced the social media calls, stressing that irregular border crossings are “risky and dangerous.”
In a statement warning of “false information and social media rumors,” UNHCR said it does not encourage or support “irregular movements,” and noted that states have the right to manage their borders.