Unrest flared briefly at a crowded reception center in the border region of Roszke, with a police spokesman saying tear gas had been fired.
Police said a record 2,533 migrants – most of them from Syria, Afghanistan and Pakistan – were caught entering Hungary from Serbia on Tuesday. Another 1,300 were detained just by 9.30 am (0330 EDT) on Wednesday, accorging to Reuters.
More will have passed unnoticed, walking through gaps in an unfinished barrier to a Europe groping for answers to its worst refugee crisis since World War Two.
Hungary, which is part of Europe’s Schengen passport-free travel zone, is building a fence along its 175-km (110-mile) border with Serbia in a bid to keep them out.
Government spokesman Zoltan Kovacs said parliament would debate next week whether to deploy the army.