The European Union's top court ruled on Thursday that Poland, Hungary and Czechia were in breach of a migrant law by refusing to host refugees streaming into southern Europe.

The verdict by the European Court of Justice (ECJ) relates to an emergency measure agreed by the EU in 2015 to relocate tens of thousands of refugees pouring into Greece and Italy, mostly from the Middle East and North Africa.

The law, which ran its course in 2017, was opposed by the three Central European states.

Their refusal to accept migrants led to the European Commission seeking an explanation, but it received no satisfactory reply.

"By refusing to comply with the temporary mechanism for the relocation of applicants for international protection, Poland, Hungary and the Czech Republic have failed to fulfil their obligations under European Union law," the Luxembourg-based court said.

The ECJ rejected the argument that the trio were within their rights to disregard EU law over public safety concerns.

It added they "can rely neither on their responsibilities concerning the maintenance of law and order and the safeguarding of internal security, nor on the alleged malfunctioning of the relocation mechanism to avoid implementing that mechanism."

The refugee crisis triggered a diplomatic meltdown in the bloc after front-line states Italy and Greece complained about the lack of consensus between member states to share the burden of the mass arrivals.

More than a million people landed on the continent's shores from across the Mediterranean in 2015, as hapless European leaders struggled to come up with measures to stem the flow.

Since then, a series of steps have been taken to crack down on illegal immigration – including financial aid to Turkey, from where most the asylum-seekers started their perilous journey.