Greece will start sending migrants back to Turkey today as part of an EU agreement to control the mass influx of people in Europe.

Around 750 mostly from Pakistan and Afghanistan, are expected to be returned as part of the deal.

But there are concerns there will not be enough staff to handle it as border management agency Frontex has reportedly only recruited a tenth of the 2300 officers it needs to do the job.

The agency relies on the EU's 28 member states to provide translators and other officials to process asylum seekers.

However, these have not been forthcoming, even as the continent faces its worst refugee crisis since the Second World War.

Under the agreement, migrants arriving illegally in Greece will be returned to Turkey if they do not apply for asylum or if they make an asylum claim that is rejected.

For every person sent back, EU countries will take in one Syrian refugee confirmed to have made a legitimate asylum request.

The deal was originally supposed to take effect immediately, on March 19, but has faced delays due to the shortage of personnel and other problems.

On Sunday another 514 migrants arrived in Greece bringing the total number in the Aegean islands to more than 6,000.

Giorgos Kyritsis, a spokesman for the Greek government's refugee crisis committee, said: "We do not know how this operation will proceed.

"This is being done for the first time and it raises unprecedented legal issues as well."

The Greek government must also deal with more than 46,000 migrants and refugees now on the mainland.

More than 20,000 live in makeshift camps on the northern border with Macedonia and in Athens.