At the same time, some 2,980 people have perished or disappeared trying to make the perilous journey, the UN's refugee agency (UNHCR) said.
The agency put the number of migrant arrivals by sea at nearly 515,000 since January 1, noting that 54 percent of that group were Syrian.
Syrian nationals made up 71 percent of arrivals in Greece, UNHCR further said.
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The four-year civil war in Syria has forced about four million people to flee the country and internally displaced more than seven million others.
The European Union is facing rising pressure to form a unified strategy for handling the influx of migrants.
Many European leaders, including in Greece, have also increasingly called for renewed efforts to forge a peace deal in Syria, describing that as the only permanent solution to the migrant crisis.
After Greece, Italy has received the most migrants in Europe since January 1, with 129,000 arrivals by sea.