According to data provided by the Greek port authorities, 68 refugees have died this month trying to make the crossing. Angelos Tzortzinis / AFP / Getty Images

Refugees land at Lesbos after the sinkings. At least 17 people, including 11 children are believed to have died in the incident. Aris Messinis / AFP / Getty Images

The Greek coast guard searches the sea for signs of other survivors. Aris Messinis / AFP / Getty Images

Greek medics worked to revive several children on the shore of the island after the boats capsized. Angelos Tzortzinis / AFP / Getty Images

Doctors try to revive a young boy after a boat with refugees sank while trying to sail from Turkey to Lesbos, Greece, Oct. 28, 2015. Aris Messinis / AFP / Getty Images

An extensive search was underway off a Greek island Thursday for at least 34 people missing after their boat sank, in the latest maritime disaster resulting from a large increase in refugees attempting to make theri way to Europe.

Five children, two men and one woman were known to have drowned after the wooden boat, crammed with more than 280 people, sank north of the Greek island of Lesbos on Wednesday.

Some 242 people on board the wooden vessel were safely plucked out of the sea after it sank about 3 kilometers north of the island, the coastguard said.

More than 500,000 refugees and migrants have entered Greece through its outlying islands since January, traveling on to central and northern Europe in what has become the biggest humanitarian crisis on the continent in two decades.

Lesbos, which lies less than 10 km from the coast of Turkey, has been a primary gateway for thousands of migrants crossing the European Union's outermost border. There has been a surge recently as migrants attempt to beat bad weather for sea crossings.