"Around 7,600 migrants, mostly from Syria, entered Macedonia between 6:00 pm Thursday and 6:00 am today," Alexandra Krause of the UNHCR refugee agency told MIA.
"We have information from our Greek colleagues that more migrants are travelling towards the Macedonian border in buses," she added.
Some 500 migrants per hour, including refugees fleeing conflicts in the Middle East, were arriving in Macedonia, according to humanitarian workers and AFP journalists.
Once arriving in the former Yugoslav republic, they walk to a reception centre set up by the UNHCR where they register with the authorities and later board buses that take them north to the border to Serbia. From there they enter Hungary, a European Union member.
More From This Section
Meanwhile, yesterday's incessant rain had stopped, making the migrants' difficult situation marginally more bearable.
Along with Serbia, Macedonia has become a major transit country for tens of thousands of migrants who trudge up from Greece, after risking their lives crossing the Mediterranean crammed into makeshift boats.
The majority are heading for Germany, which has pledged to welcome hundreds of thousands more refugees having already taken in 450,000 to date since January.
Meanwhile, in Presevo, on the Serbian border, hundreds of migrants were waiting to obtain documents allowing them to continue their journey through the Balkan country.
The former Syrian police officer from the northern town of Aleppo was hoping to get to Germany. His father, brother and sister were accompanying him on the long and dangerous journey.
"The only goal of this exodus is to survive," added Wahid Rashid, 37, while trying to dry his passport holding it above an improvised camp fire.