ATHENS, Greece — Hundreds of people using small boats and dinghies have arrived over the past day on the eastern Aegean islands near the Turkish coast, Greek authorities said Tuesday, part of a surge of tens of thousands of migrants landing on Greek shores in recent months.

The coast guard said 457 people had been rescued from the sea in 12 separate cases off the islands of Lesbos, Chios, Kalymnos and Kos in 24 hours from Monday morning. Another 304 people had made their way ashore Monday to Lesbos' main port of Mytilene.

With some of its islands just a mile or two off the coast of Turkey, Greece and its islands are a major entry point for migrants and refugees from Asia, Africa and the Middle East hoping for a better life in the European Union.

Few want to remain in the debt-stricken country where unemployment runs at above 26 percent, with most making their way to the more prosperous countries of Europe's center and north. They usually travel by land across Greece's northern border with Macedonia or cross the Ionian and Adriatic seas smuggled aboard ferries to Italy.

The increase in the number of people arriving in Greece has been dramatic. The International Organization for Migration said 46,150 migrants had already arrived in Greece in the first five months of this year, compared to about 34,000 for the full year 2014. Most, it said, were Syrians and Afghans.

The U.N. refugee agency, UNHCR, had slightly different figures, saying 48,000 refugees and migrants had reached Greece so far this year, the second-largest number in a EU nation after Italy, where 54,000 people have arrived.

About half of those arriving in Greece were coming ashore in Lesbos, UNHCR spokesman Adrian Edwards said during a briefing in Geneva. He said arrivals there had swelled to more than 7,200 in May.

Greece has long called for more assistance from the rest of the EU to deal with the influx, saying it cannot bear the brunt of the refugee and migration crisis alone.