Hundreds of migrants have managed to breach the Greek-Macedonian border, further along from where the main crossing is closed.
As many attempted to get across a swollen river, tragedy struck: Macedonian police say two men and a woman drowned.
Officials say they are now taking steps to return the migrants who managed to get across into Macedonian territory.
More than a thousand migrants earlier left a camp near the border in northern Greece, frustrated at the virtual closing of the so-called Balkans route.
MSF Sea (@MSF_Sea) March 13, 2016
The border breach is reported to have happened north of the Greek town of Chamilo, and the bodies of the migrants who drowned were found across the border near Gevgelija.
Also on Monday eight migrants were reported missing after a boat sank off the Greek island of Kos.
Migrants are still arriving in Greece despite the border closures and a bottleneck of thousands of people, including the elderly and children.
A complex draft agreement between the EU and Turkey over how to stem the flow of migrants will be debated at a summit in Brussels this week.
However, there are obstacles to overcome, with a question mark over the legality of the plan and the practical aspects on the ground.
Euronews’ Nicoleta Drougka reported from Athens: “Constant rain has made things dramatically difficult for the refugees.
“Doctors are very concerned. Especially for the thousands of little children, who get sick all the time with the flu or gastroenteritis. They are almost impossible to treat in these terrible living conditions.
“Children amount for roughly one third of the refugees, who now number about 45,000 throughout Greece.
“Of these, 12,000 are still in Idomeni, 10,000 on the islands,11,000 in the Athens area and 12,000 in the rest of mainland Greece.
Meanwhile, arrivals continue. Turkish media say about three million refugees and migrants are on the Turkish coast, waiting for the opportunity to cross to Greece.”
#Refugees leaving #Idomeni, Greece, FYROM border, into rivers, for the mountains v.— Stratos Safioleas (@stratosathens) March 14, 2016
MovingEurope</a> h/t <a href="https://twitter.com/RafiqCopeland">RafiqCopeland pic.twitter.com/g0Vf2Rd9uW
#MarchOfHope leaves Idomeni:
AmnestyOnline</a> gallery portrays life there <a href="https://t.co/7qJSTGP5yl">https://t.co/7qJSTGP5yl</a> <a href="https://twitter.com/hashtag/StopTheDeal?src=hash">#StopTheDeal</a> <a href="https://t.co/DyqnVhhg2a">pic.twitter.com/DyqnVhhg2a</a></p>— amnestypress (amnestypress) March 14, 2016