Up to 2,500 refugees in Kos were locked in a stadium for nearly 24 hours, after riot police struggled to contain crowds of recent migrant arrivals rounded up from makeshift camps around the Greek island.

On Wednesday afternoon, after being locked inside for about 18 hours, the mostly Syrian and Afghan refugees were fainting at a rate of four each hour, aid workers said.

About 1,000 of the refugees were trapped inside a playground within the stadium complex, with no access to water or shade. A further 1,500 were housed in a separate section of the stadium, with some protection from the sun.

Constance Theisen, a team leader for Médecins sans Frontières, which was providing medical care at the stadium, told the Guardian: "We have unconscious people coming out of the playground area, being carried by their friends and family, every 15 minutes. It is absolutely out of control. Nobody understands the sense behind it, or if there is any [sense] at all."