More than 7,000 refugees and other migrants are camped on Greece's northern border with Macedonia, waiting for authorities to allow them to continue their long trek north to seek asylum in wealthier European countries.

The Idomeni crossing has been closed for nearly 24 hours, following clashes when hundreds of migrants tried to force their way into Macedonia, whose police responded with tear gas and stun grenades.

On Tuesday, hundreds of small tents stood in the fields around an official migrant camp on the Greek side of the border that can take no more people.

Some migrants have been waiting at Idomeni for more than a week, as even when the border is open Macedonia allows in no more than a few hundred, citing a similar policy by Serbia further north.

A group of about 150 people who have been told they can enter Macedonia have spent days in a large tent in front of the crossing.

"I've been at Idomeni for 10 days, and it's the fourth day I've been waiting to cross over," said Hassan Rasheed, 27, from Iraq.

"Conditions are very bad. There are many ill children who are coughing, and we spent the night in this tent under heavy rain."

Small groups of refugees have been arriving at the border in a steady flow, mostly on foot after walking up to 18 miles along highways.

Among them was Ahmed Majid, a 26-year-old Iraqi travelling with his wife and two children.

He said: "We have been walking for three kilometres. Police stopped our taxi on the national road, which is why we are going through the fields.

"On the route from Athens police kept stopping us at petrol stations and told us that the border was still shut."

Meanwhile, Greece has deported a group of 69 economic migrants from north Africa back to Turkey at the Kipi border crossing. A further 230 people are due to be sent back by Wednesday, mostly Moroccan, Algerian and Tunisian nationals.