The number of migrants awaiting passage to central and northern Europe swelled on Greece's border with Macedonia on Wednesday as the frontier remained shut, adding to a humanitarian crisis and deep fissures within the European Union.
Aid workers said the situation at Idomeni, a small border town in northern Greece, could easily spin out of control with no let-up in the number of refugees gathering for passage into Macedonia.
Living in filth, families with small children jostled for space in waterlogged fields, waiting for a crack in the border fence, which Macedonian authorities opened intermittently.
By midday on Wednesday the border had opened once, Greek police said, allowing 170 people through.
"There are 11,000 people here and conditions are very bad," said Antonis Rigas of charity Medicins Sans Frontieres.
"We worry that if it exceeds 12,000 the situation might get out of hand," he said.
Macedonian authorities have defended their stance. "Our daily admittance of migrants will depend on how many will be accepted in EU countries," Interior Minister Oliver Spasovski, told reporters in Skopje.
"It is very important to secure humane treatment and admit these people, but it's no less important that we protect the Macedonian citizens and police."
Macedonian police fired tear gas to disperse hundreds of migrants who stormed the border from Greece on Monday, tearing down a metal gate.
The European Union has called an emergency summit with Turkey on March 7, hoping for a consensus to implement an accord on the distribution of refugees and migrants fleeing conflict and poverty in the Middle East, North Africa and beyond. Many arrive in Greece on small, unsafe, boats from Turkey.
More than one million people fled Syria, Iraq and Afghanistan last year. Around 131,000 have reached Europe so far in 2016.
At Idomeni, a grassy plain, a tent community was growing rapidly in the mud, stretching resources to the limit. The average wait for a small package of food consisting of a sandwich and a boiled egg was two to three hours.
Some people had no shelter.
"We will sleep on the ground," said Hassan Fatahalla, 25, from Idlib in northwest Syria, who arrived at the camp with his wife Shakeri, nine months' pregnant. "We want to go to Germany ... it will be a better future for the baby."
People continued to arrive as dusk approached, many of them on foot. An elderly couple, both in wheelchairs, made their way to the makeshift camp. A younger family emptied a wheelie bin and placed their two children in it, rolling it down the road.