More than a thousand migrants crossed into Serbia from Macedonia early today near the village of Miratovac.
They follow the more than 5,000 people who crossed into Serbia yesterday after an overwhelmed Macedonia gave up its attempts to stem the flow of mainly Syrian refugees by force.
Macedonia declared a state of emergency on Thursday and sealed its southern frontier to migrants pouring in at a rate of 2,000 per day.
The numbers had overwhelmed the main border railway station and the conservative government, which has a tense relationship with Greece, said enough was enough.
That led to desperate scenes at the border before crowds finally tore through police lines on Saturday.
The migrants, from the Middle East, Africa and Asia, are expected to continue their journey further north and cross by foot into Hungary and Europe's borderless Schengen zone.