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.

Hundreds of small tents stood Tuesday 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.