The United Nations' refugee chief Friday, September 4, for Europe to mobilize its "full force" in tackling its migrant crisis, just as Hungary's right-wing leader told Europeans they risk becoming a minority on their own continent.

Declaring that the European Union faces a "defining moment", the head of the UN refugee agency Antonio Guterres said a divided bloc would benefit only smugglers and people traffickers.

His appeal for EU states to do more in helping migrants - many of them refugees fleeing the Syrian civil war - contrasted with the tough line from Hungarian Prime Minister Viktor Orban, who warned about the consequences of "a mass inflow of people", possibly numbering tens of millions.

Guterres said the EU needed to help more migrants enter legally and provide about 200,000 relocation places, according to a preliminary estimate, as well as support countries under pressure such as Greece, Italy and Hungary, Reuters says. "It now has no other choice but to mobilize full force around this crisis. The only way to solve this problem is for the Union and all member states to implement a common strategy, based on responsibility, solidarity and trust," he said in a statement.