ATHENS, Greece -- Greece's coast guard rescued hundreds of migrants in more than a dozen search-and-rescue operations, including one in which a toddler found unconscious in an overcrowded dinghy died, authorities said Wednesday.

The coast guard said it picked up 534 migrants off the eastern Aegean islands of Lesbos, Chios, Agathonissi, Samos, Farmakonissi and Kos in the 24 hours to Wednesday morning -- and another 108 during the day Wednesday off Agathonissi and Chios.

Those numbers do not include the hundreds more who managed to reach the islands on their accord in overcrowded dinghies.

Separately, it said a little boy of about 2 or 3 years old was found unconscious in a dinghy spotted by a patrol helicopter carrying 54 migrants off Samos. A coast guard vessel picked the group up and the child was taken to a hospital, but he died, the coast guard said. Authorities said an autopsy would be carried out.

Greece has seen record numbers of migrant arrivals this year, most fleeing conflicts in Syria and Afghanistan and arriving on Greek islands from the nearby Turkish coast. About 160,000 migrants have reached Greece so far since January, compared to 43,500 for all of 2014, according to figures from the U.N. refugee agency. More than four-fifths are from Syria.

While cheap inflatable dinghies with small engines are the predominant method used by smugglers to reach Greek islands, groups of migrants have also paddled the several miles separating some of the islands from the Turkish coast. One smuggler was arrested Wednesday after transporting two migrants to Lesbos on a jet ski, the coast guard said.

Few -- if any -- of those who arrive want to stay in Greece, which is reeling from a financial crisis and has an unemployment rate of more than 26 per cent. Instead, they head to Greece's northern border with Macedonia, cross the Balkans and head to more prosperous European countries, particularly Germany and the Scandinavian countries.

Short-staffed and cash-strapped authorities on islands have been overwhelmed with the sheer numbers of daily arrivals.

With the tourism season at its peak, another problem has arisen -- regular ferries are fully booked with holidaymakers, meaning thousands of migrants have been unable to find tickets to get to the Greek mainland.

Hundreds of migrants have been camping out for days on Lesbos and other islands. Authorities chartered a ferry this week to Kos, one of the most severely affected Greek islands, using it as an accommodation and registration centre for migrants.

The ferry set sail Wednesday from Kos with 1,308 migrants and headed to nearby Leros where it picked up hundreds more. It was continuing on to Lesbos to pick up some of the hundreds of migrants stranded there before setting sail for Athens.

The ship, which had been scheduled to sail to the northern port of Thessaloniki, was expected to arrive instead in the Greek capital's port of Piraeus early Thursday, the coast guard said.