The operation began at dawn and witnesses reported police vehicles and buses standing by to transfer people to better organised facilities.

Hundreds of riot police have been deployed but officials say force will not be used.

At least 8,400 people - many of them women and children - are at the camp.

Most of them had been on their way to northern Europe when they became stranded after Macedonia closed its border with Greece.

They have been promised much better facilities at newly-created asylum processing centres near Greece's second city Thessaloniki.

At least four bus loads of migrants were seen leaving the camp on Tuesday morning, with others leaving on foot or by taxi.

Police prevented journalists entering the camp on Tuesday morning but at least 20 police vans were seen going in while a police helicopter monitored the operation.

Giorgos Christides, a journalist at the camp for the German magazine Der Spiegel, told the BBC that police were determined to clear one part of the camp on Tuesday.

They are planning to complete the operation within 10 days, he added.

Speaking on Monday, government spokesman Giorgos Kyritsis told Greek television all migrants would be moved.

"A thing like Idomeni cannot be maintained. It only serves the interests of smugglers," he said.