Approximately 2,500 refugees in Greece have been locked in a stadium for almost a day, as local riot police battled to control hoards of the recently arrived migrants.

Aid agencies said refugees were locked in the stadium for 18 hours with no water, access to shade or toilets, resulting in people fainting at a rate of four per hour.

The unrest has led to riot police clashing with the refugees who are frustrated and angry at the time it is taking for them to be registered on the island of Kos.

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About 1,000 of the Syrian and Afghan refugees were trapped in a playground area of the stadium, The Guardian reported.

“We have unconscious people coming out of the playground area, being carried by their friends and family, every 15 minutes,” Médecins sans Frontières team leader Constance Theisen told The Guardian.

Women and children wait to have there claims processed while riot police hover. Photo: Getty

“It is absolutely out of control. Nobody understands the sense behind it, or if there is any [sense] at all.”

The aid group said one of the migrants had an epileptic seizure.

Migrants were initially locked in the stadium in the evening to go through a registration process, however MSF said just three police officers were present to carry out the administration work.

This exacerbated tensions which led the police to leave. More authorities including riot police, then arrived in the morning.

Médecins sans Frontières spokeswoman Julia Kourafa said it was the first time she had ever witnessed this in Greece.

“We’re talking about mothers with children and elderly people. They’ve been locked in there after many hours in the sun,” Ms Kourafa said.

After about 20 hours authorities opened up shaded areas and provided portable toilets for the refugees.

Some 120,000 refugees have arrived on various Greek Islands since the start of 2015. That is up from 30,000 in 2014.

Most make the short boat journey from Turkey, with the majority escaping war torn areas of the Middle East including Syria and Afghanistan.

Authorities have been battling to register the refugees on the Greek Islands properly, before taking them to Athens so they can move to other parts of Europe.

Greek prime minister Alexis Tsipras said the country, already battling economic crisis, just did not have the infrastructure to deal with the influx.