Migrants cradling young children blocked a motorway in central Greece demanding onward passage to Former Yugoslav Republic of Macedonia (FYROM) on Wednesday, part of a growing bottleneck of refugees stranded by new border restrictions and closures across Europe.
Families chanted "We want to go" after police stopped their convoy at Tempe and authorities stepped up measures to control the flow of people passing through the country on their way to more prosperous nations further north.
Reuters journalists saw hundreds of others gathered at petrol stations and motels along the 530-km (330-mile) route from Athens to FYROM, where guards periodically opened the border on Wednesday morning, letting 100 people through at a time.
Greece has protested against restrictions imposed by countries further north along the main land migration route into Europe.
Migrant Minister Yannis Mouzalas singled out controls brought in by Austria, Slovenia, Croatia, Serbia and FYROM after a meeting of their police chiefs last week.
"It's scandalous… that five police chiefs can overturn a decision of European Union prime ministers on the matter," Mouzalas told Reuters in Athens.
Austrian Foreign Minister Sebastian Kurz brushed off criticism of his country's plans to impose daily caps on migrants, saying on Wednesday that Greece needed to do more to reduce the flow.
More than a million migrants and refugees passed through Greece last year, many of them fleeing conflicts in Syria and Afghanistan.
Another 1,600 arrived on the mainland from outlying islands bordering Turkey on Wednesday morning.
Two Greek government officials said there were an estimated 20,000 migrants stranded in the country.
"When there is a bottleneck, the bottle could break, and where we had a controlled movement of individuals … a broken bottle could result in an uncontrolled, illegal influx," Mouzalas said.
Balkan decisions to halt the flow would escalate, and not reduce, illegal migration, he added.
Greek police had orders to stop buses carrying migrants to Idomeni, at the border with FYROM, on Wednesday.
"Nobody will leave for Idomeni today. I will not allow a single bus to leave for the north until further notice that Skopje is allowing people through," said Konstantinos Louziotis, head of the public order ministry's immigration department.
One driver in a convoy of eight buses carrying migrants to the FYROM border told Reuters they were stopped by police and asked to sleep at a stadium on Tuesday night.
About 1,000 people were gathered in a field at the frontier on Wednesday, 24 hours after another group of migrants had been rounded up and removed from the area by Greek authorities.
At Piraeus port, Syrian migrant Hasan Frnjari said authorities had told him to stay there until further notice.
"We came here in the morning and don't know what to do because we want to continue to Macedonia. Now they tell us the borders are closed," said the 23-year-old marketing student from the northern Syrian city of Aleppo.
"I don't think they really understand the cause we left from Syria, in Aleppo people are in danger. The city is under constant shelling. You walk in the street and you can die just like that."