The United Nations refugee agency says an estimated 42,000 migrants have reached Greek shores since the start of the year — six times more than in the same period last year and almost as many as those arriving in Italy.

The number is close to the total arriving in Greece for the full year 2014. Most were from war-torn Syria, Afghanistan, Iraq, Somalia and Eritrea, UNHCR said.

The agency said Friday it is sending extra staff to assist authorities in Greece's eastern Aegean Sea islands, where an average 600 people have been arriving every day this year in small, unseaworthy craft.

Italy received 46,500 as almost 90,000 people crossed the Mediterranean from January-May, and at least 1,850 died or went missing.