At least 300 migrants have been injured after violent clashes with authorities at the Macedonian border with Greece, charity Médecins Sans Frontières‎ (MSF) said.

Authorities in Macedonia have been accused of using "dangerous and deplorable" force against migrants protesting at the Greece's border town Idomeni.

"The situation was extremely tense this morning, when tear gas, rubber bullets and stun grenades were used in the camp to disperse crowds. The MSF teams treated 300 people, among them 200 with respiratory problems after being subjected to teargas," the charity said in a statement.

Police sources say tear gas was fired only after migrants stormed towards a border fence on Sunday.

The EU is now deporting new arrivals to Greece back to Turkey if they don't meet asylum criteria after agreeing a deal with the country.