Four central European countries on Wednesday called on the European Union to let member states decide for themselves how many migrants they will accept, instead of setting quotas.

"The voluntary principle is a clear priority" of the Visegrad Four countries, the prime ministers of the Czech Republic, Hungary, Poland and Slovakia said in a joint statement.

Calling for a "more systematic and geographically more balanced solution to the migration crisis", the countries said all EU members should take part in weathering the critical situation on the bloc's borders, which are tested daily by hundreds of migrants from Africa and the Middle East.

But they also slammed the current debate on migration, saying "any relocation measures should be taken on a voluntary basis... respecting the specifics and capacities of the individual member states".

"We affirm that any request for mandatory quotas is unacceptable for us," reads the statement, expressing at the same time solidarity with "those EU members that are the most exposed to migration pressures".

Just ahead of an EU summit on migration scheduled for Thursday and Friday, the Czech Republic, Poland and Slovakia said separately that they would accept migrants but not on the basis of quotas.

Hungary, which has seen 60,000 migrants crossing its border this year, said it would build a four-metre (13-foot) fence on its southern border with Serbia through which most migrants come into the country.

Hungary sparked uproar on Tuesday by opting out of an EU asylum rule requiring migrants' claims to be processed in the EU country they first arrive in.

But its foreign minister said Wednesday that the country was "not suspending any rule" and had merely requested a period of grace.