The expulsion launches a controversial EU deal to send migrants back across the Aegean Sea that has been criticised by rights groups on ethical grounds.
Two Turkish leisure vessels on Lesbos and another one on Chios are waiting to pick up the migrants, who are to be escorted by police from EU border agency Frontex.
On Lesbos, crews were earlier seen loading supplies onto the ships -- a small ferry and a catamaran.
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Turkish Interior Minister Efkan Ala has said his country is ready to receive 500 migrants on Monday and Greek authorities have provided 400 names, although these numbers could change.
The European Union signed the controversial deal with Turkey in March as it wrestles with the continent's worst migration crisis since World War II, with more than a million people arriving last year.
Under the agreement, designed to halt new arrivals along the most popular route through Turkey, all "irregular migrants" arriving since March 20 face being sent back. Each case is meant to be examined individually.
For every Syrian refugee returned, another Syrian refugee will be resettled from Turkey to the EU, with numbers capped at 72,000.