© Yorgos Karahalis/AP Police on Tuesday tried to disperse hundreds of migrants by spraying them with fire extinguishers during registration in the stadium.
Several of the refugees, who are mostly Syrian and Afghan, fainted due to heatstroke, and one had an epileptic seizure, said the aid group MSF, which was providing medical care at the stadium. At one point the police used a sonic explosion to maintain order, and the MSF team withdrew for safety reasons.
Julia Kourafa, a spokeswoman for MSF at the stadium, said: "It was becoming a bit uncontrollable, the situation, and there was a complete lack of coordination. It was just the police there, no UNHCR [the UN's refugee agency], and no security for [our] team."
Kourafa added: "This is the first time we've seen this in Greece - people locked inside a stadium and controlled by riot police. We're talking about mothers with children and elderly people. They've been locked in there after many hours in the sun."
The migrants were originally locked inside on Tuesday night ostensibly to be registered. But, according to Kourafa, just three police officers were there to carry out the registration, slowing the process down, and exacerbating tensions, leading to MSF's withdrawal at around midnight. They returned early the next morning to provide medical assistance, but the refugees remained locked inside. Little, if any, food or water had been supplied by the Greek authorities, and refugees continued to faint.
Tensions were also rising fast on several other eastern Greek islands, where over 120,000 refugees have arrived since the start of the year - up from around 30,000 during the whole of 2014.
Having made the short boat crossing from Turkey to the EU, the refugees are frustrated to find themselves essentially trapped on the Greek islands. The Greek authorities are attempting to register them all before they are taken to Athens and tacitly allowed to move onwards through Europe.
But due to the unprecedented scale of the crisis, Greek police have been unable to process them fast enough, leading to bottlenecks on islands such as Kos.
At times, the authorities have been unable to supply enough food, and do not have enough space to house so many migrants, with over 1,000 new arrivals landing from Turkey every morning. Greek prime minister, Alexis Tsipras, said last week that the country, already battling an economic crisis, lacks the infrastructure to deal with a migration one.
Despite the situation on the islands, many of the 1.6 million Syrian refugees currently in limbo in Turkey are still planning to make the journey to Greece. Mousa, a former English literature student planning to reach Kos by the end of the month, said he was undeterred, despite watching a video of the scene at the stadium. He said this was because he intended to buy a fake EU passport on arrival in Kos, rather than register as a refugee with the Greek government.
Mousa said: "I'd still go because, the way I've planned it, I'm getting to Kos and then going straight to the airport and off to [another EU destination]. I'm not going to deal with authorities in Greece."
Much of the humanitarian effort to help the refugees, who are mostly fleeing wars in Syria and Afghanistan, has been shouldered by local volunteers and NGOs. The lack of resources and the slow pace of registration has led to protests and sporadic clashes with police. Before the migrants were locked overnight in the stadium, Kos police used fire extinguishers to force back a group of protesting migrants. Earlier in the summer, the Greek army was forced to keep order and provide extra supplies at a migrant camp on the island of Lesbos, where the civilian authorities had run out of food to feed the residents.
The Ekatimerini newspaper reported that a dozen extra immigration officers, including Arab speakers, have been sent to Kos this week to help speed up the identification and registration of 7,000 mostly Syrian migrants now thought to be on the island.
Two units of riot police have also been flown to the island, national police chief Dimitris Tsaknakis told the paper, while a further 250 regular officers were on their way to Kos and the other eastern Aegean islands of Lesbos and Samos.
The Greek islands are now the main point of entry for migrants seeking to reach Europe by boat. The number of migrants arriving there has outstripped the equivalent rate in Italy, which was traditionally the principle gateway for maritime migrants. The migrant arrival rate is still at record levels in Italy, but it has still welcomed around 20,000 fewer asylum seekers than Greece in 2015.
There are also fears of bottlenecks at the other end of Greece, at its northern border with Macedonia. Macedonian soldiers briefly closed the border in June, blocking the exit route for thousands of refugees hoping to reach northern Europe, and raising the spectre of a more permanent border closure in the future.
MSF's director of operations, Brice de le Vingne, said: "MSF is very worried about how the situation is evolving in Kos. What was previously a situation of state inaction is now one of state abuse, with police using increasing heavy handed force against these vulnerable people.
"The great majority of people arriving here are refugees fleeing war in Syria and Afghanistan. The Kos authorities have clearly stated that they have no intention of improving the situation for these people as they believe that this would constitute a 'pull factor'. But the truth is that people fleeing war will keep on coming whether or not the authorities are trying to stop them from doing so."
At the time of writing, Kos's mayor, Giorgos Kyritsis, had not returned requests for comment by telephone.
What to do with people considered 'unnecessary'? ...with people that no one wants? So many of them, good thing they're not Jewish, or we'd have to create a homeland for them somewhere.... perhaps 'over the rainbow? Is that the goal?