Greek authorities say a seven-month-old Syrian baby temporarily staying with its family in a refugee registration camp on the island of Lesbos has died, apparently of natural causes.

Health officials will try to determine the precise causes of the baby's death later Wednesday.

Lesbos, in the Aegean Sea, is the main arrival point for the nearly 850,000 migrants and refugees who have arrived in Greece this year, paying smuggling gangs to ferry them over from nearby Turkey in frail boats.

Few want to stay in Greece, preferring to continue north through the Balkans to wealthier European countries. Balkan states have started refusing entry to suspected economic migrants, and identity fraud is rife.

On Tuesday, police on Lesbos arrested a man suspected of planning to sell fake registration papers to migrants.