Refugees and migrants in Greece have staged protests at the country's border with Macedonia and on islands near the Turkish coast, as officials still are unsure when an international agreement to reduce migration would take full effect.

Several hundred protesters camped out at the border disrupted food distribution by charities on Wednesday, and demanded the border be reopened.

Small protests have also occurred at three detention camps on three Greek islands, where arrested migrants and refugees are waiting to be deported back to Turkey.

All refugees and migrants arriving in Greece are being arrested since Sunday, when the agreement between Turkey and the European Union took effect.

Greek officials could not say when the deportations would start, with outstanding legal and practical issues still to be resolved.