Some 170,000 irregular migrants entered the European Union in September, the bloc's border agency Frontex said on Tuesday, taking the total for the year so far to 710,000.
That compares to 282,000 migrants crossing EU borders irregularly for the whole of 2014 as Europe faces its biggest refugee crisis since World War II.
In August, Frontex said in its latest statement, it recorded 190,000 irregular arrivals, many of them by sea to Greece, setting a fifth consecutive monthly record. In all, 350,000 people reached Greece from January to September, of whom 49,000 arrived in September alone, many of them Syrians.
A shortage of boats in Libya and worsening weather helped to 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 European Union's struggles to deal with the flow of migrants 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.