Croatia has banned Serbian vehicles from entering its territory in response to a Serbian ban on Croatian cargo traffic in a bitter dispute over the flow of refugees across the border.
"Our border is ready and open for any other car without Serbian registration. Buses with Serbian registration will not enter into Croatia," Croatian Interior Minister Ranko Ostojic said.
Ostojic said there had been "a problem with passports" but confirmed that Serbian citizens were still free to travel across the border.
Serbia issued its ban on Croatian cargo traffic and goods late on Wednesday as relations plunged to their lowest since the overthrow of Slobodan Milosevic in 2000.
Meanwhile, Hungary has said it had received a record number of refugees in a single day, with most entering via Croatia.
Some 9,939 refugees arrived from Croatia on Wednesday, while 102 arrived from Serbia, AFP reported, citing Hungarian police.
The latest EU emergency summit has to done very little to solve the refugee crisis other than create bitter arguments between members.
European leaders have been told their collective pledge of more than one billion euros will not end an accelerating refugee crisis.
Mahmoud Elawi enjoyed a comfortable life before war turned his family's life upside down. Now he wants to thank Britain for its compassion.