Thousands of people, including many families with young children, are braving torrential downpours to cross Greece's northern border with Macedonia, after Greek authorities managed to register about 17,000 people on the island of Lesbos in the space of a few days, allowing them to continue their journey north into Europe.

Greece's caretaker government chartered two extra ferries and sent additional staff to Lesbos to speed up the registration and ease overcrowding on the island, where more than 20,000 refugees and migrants had been living in precarious conditions after arriving on dinghies from the nearby Turkish coast.

About 7,000 people waited in the mud of an open field near the northern village of Idomeni to cross the Macedonian border early Thursday, with more arriving in trains, buses and taxis.