EU border agency Frontex said Tuesday that 710,000 people fleeing war and poverty entered the European Union in the first nine months of this year — more than double the number in all of 2014.
Frontex said that in September alone, some 170,000 people were detected entering the bloc, as Europe faces its biggest refugee crisis since World War II.
Some of the increase may reflect double counting, likely because of a surge in people arriving in Greece, then crossing non-EU Balkan nations and re-entering the EU in Hungary.
And September's total lower than the record 190,000 arrivals recorded in August.
The rapidly collated figures on detected arrivals provide a rough monthly snapshot of migration flows. Statistics on asylum claims in the EU, which lag, showed some 400,000 people claimed protection at the bloc's borders in the first half of this year, compared with 625,000 in all of 2014.
In all, 350,000 people reached Greece from January to September, Frontex said, of whom 49,000 arrived in September, many of them Syrians.
A shortage of boats in Libya and worsening weather helped halve the number of migrants arriving in Italy in September, to 12,000, Frontex said, bringing the total for the first nine months in Italy to 129,000, many of them from Eritrea.
The figure for irregular border crossings includes significant double counting. In the nine months through September, Hungary reported 204,000 people crossing its borders who did not have appropriate passports or visas. That was a 13-fold increase from the same period in 2014. But, a Frontex spokeswoman said, many of those entering Hungary would have been recorded entering Greece before moving on through the Balkans.
September's EU aggregate did not yet include an estimated 97,000 people who entered the EU in Croatia in the second half of last month after Hungary sealed its border with non-EU Serbia, Frontex said in its statement.
The European Union's struggles to deal with the flow of refugees fleeing poverty and turmoil in the Middle East and Africa has plunged the 28-nation bloc into crisis.
Leaders are due to discuss their responses again at a summit in Brussels on Thursday and Friday. Among items on the agenda are closer cooperation with Turkey, from which many Syrian refugees reach Europe, and beefing up Frontex's ability to support national border guard services to control arrivals.
"Urgent assistance is needed, especially for Greece and Italy, to help register and identify the new arrivals," the border agency's executive director, Fabrice Leggeri, said, noting his request for hundreds of extra staffers for Frontex. "I do hope we receive adequate contributions, which will show the true spirit of European solidarity."
Al Jazeera and wire services