Greek police restarted an operation on Wednesday to move migrants out of Idomeni, the squalid tent city where thousands fleeing war and poverty have lived for months.

A police source said they hoped to transfer "roughly the same number" of migrants as on Tuesday, when they bussed more than 2,000 to newly opened camps near Greece's second city Thessaloniki, about 80 kilometers to the south.

Some 8,400 people are living in the muddy and dirty camp on the Macedonian border, which has become a potent symbol of human suffering and chaos as Europe struggles with its worst migrant crisis since World War II.

The dawn operation, involving some 700 police backed by helicopter, "is continuing normally and calmly, like yesterday", said the police officer, who declined to be named.

Most of those at the camp are fleeing war and misery in the Middle East and Asia and the group transferred on Tuesday included 662 Syrians, 1,273 Kurds and 96 Yazidis.

"We try to separate nationalities to avoid friction between them," said another police source.

Around 100 migrants refused to enter the new center on Tuesday and headed off by foot to Thessaloniki.

'Treated like pawns'

Non state-run media were again kept at a distance during Wednesday's operation.

On Tuesday, ERT state television and state news agency ANA showed migrants patiently queuing up to board buses and being driven away, some waving at the camera.

Many carried their belongings in huge bin bags, while others piled possessions into pushchairs.

It will take a week to complete the operation to clear all 8,400 people living there, the government said.

"It is all going well, perhaps better than we expected. The migrants are tired and no longer expect the borders to be reopened," a police source said on Tuesday.

Oxfam urged Athens to guarantee migrants have "full access" to information and medical treatment.

"Vulnerable people, the majority of whom are women and children, are being treated like pawns in a chess game," the NGO added.

The Greece-Macedonia border is one of several in the Balkans closed since mid-February.

And the transfer comes after a brutal winter of freezing rain and mud which saw many people trying to force their way across the border, sometimes resulting in violent encounters with Macedonian police.

AFP-Reuters-AP