EU President Donald Tusk on Tuesday convened an informal meeting of the bloc's leaders to speed up their response to the migration crisis, with the talks to take place straight after a summit with African states in Malta next week, dpa reported. Europe is contending with the biggest migration flows since World War II, with more than 750,000 migrants and asylum seekers arriving by sea this year. Many of them come from war-torn Syria. The European Union has begun taking steps aimed at curbing the influx, but Tusk warned in a letter to leaders that the arrivals are continuing at an "unprecedented pace." "If we are to avoid the worst we must speed up our actions," he wrote, warning that the EU's border-free Schengen zone - one of its most prized accomplishments - is at risk if the bloc fails to secure its external frontiers. The November 12 talks - to assess action taken to date and discuss ways of reinforcing external EU border controls - will take place hours after the Valletta summit, at which the 28 EU leaders are to discuss migration challenges with their African counterparts. Tusk and European Commission President Jean-Claude Juncker warned member states last week that they are not acting fast enough, in a letter made public on Tuesday. Greece and Italy - the main points of arrival to the EU - have been tasked with setting up so-called hotspots to register and fingerprint arrivals, with EU support. The aim is to separate genuine asylum seekers from economic migrants, who are to be sent back home. But member states are failing to provide the necessary staffing, Tusk and Juncker said.