These are not tourists, but refugees. And instead of looking forward to enjoying a fortnight in the sun, they're preparing to camp out in parks and on the sand, as they wait for the papers that will allow them to continue their journeys away from war, or out of poverty.
More than 7,000 migrants arrived on Kos in July, according to Doctors Without Borders, and tens of thousands more landed elsewhere in Greece in the same month, stretching the capacity of its cash-strapped government to cope, the U.N. refugee agency said.
In total, almost 160,000 refugees and migrants arrived in Greece by sea between January and mid-August this year, according to the UNHCR.
Ibrahim Najjar told CNN he had little choice but to flee his homeland: "There is nothing left for us in Syria. Only destruction."
He wants to travel on to Germany, where he hopes to find work as a waiter: "My younger brother and I made it to Turkey, then we only had money to bring me to Europe, so I had to leave him behind."
Manar, 27, and also from Syria made the hazardous journey to Greece while six months pregnant; she is hoping to be reunited with her husband in time for the birth of her baby.
"My husband made it to Sweden a few months ago. We finally got the money for me to be able to escape Syria too. The journey will be hard but we will be a family there, happy and free. There is no freedom in Syria, only bombs".
There have been dramatic changes in Kos since we were here just two months ago: In June, the migrants were arriving at a rate of about 100 people a night, but most of those we met were out of sight, living in poor conditions in an abandoned hotel, the "Captain Elias."
Fast-forward a couple of months, and it's a different picture. Migrants' tents have taken over most of the beachfront near Kos City. They are camped in squares and parks, or sleeping at the roadside.
Babies crawl between the dirty blankets while older children kick a deflated ball around and overdressed elderly men, still wearing jackets despite the 40C heat, look back across the sea to Turkey, wondering if they will ever see their homes again.
Some escape the heat by swimming in the sea, sharing the beach with tourists, most of who are bemused by the situation they find themselves in. Other holidaymakers stay in their resorts to avoid the harsh reality of island life.
Back in June, the locals were sympathetic, and many are still helping the new arrivals with food, water and toys for the children, but patience is wearing thin.
Kostas owns a restaurant in what used to be a prime position on the beachfront, next to the beautiful police station. Now, with thousands of migrants waiting for their papers on the same square, his business has gone downhill.
"I feel sorry for them, how can I not?" he says. "But now no-one comes to my restaurant, why would any tourists come here? The square is crowded, dirty and it smells of urine. It is August, it is high season and I already had to sack a cook and two waiters."
And Kostas is not alone -- other locals are feeling the burden. Stella is a street cleaner in Kos City. She says her children can't go out to play anymore.
"It is full of people we don't know, they make it all dirty, they have no toilets so you can imagine ..." she says. "I work all day picking up their rubbish and it is still dirty.
The situations the migrants fled were desperate, but many have been surprised, having survived the sea journey -- what they thought would be the toughest part of their journey -- by how difficult life on Kos is.
Many of them are sleeping rough in areas ill-equipped to deal with the huge numbers of new arrivals.
A spokeswoman for Doctors without Borders told CNN the migrants have no food or water, no shelter, and no proper toilets. "They don't want to stay here, they are completely shocked by these conditions," she says.
"They have been fleeing their country because of war, because of the bombs, and now they cannot even have a proper toilet. They are saying that maybe the bombs have been better than staying in these conditions."
Ali, 27, says he left his home in the Iraqi capital, Baghdad, fearing for his life: "I was a police officer in Iraq but I had to leave; if I stayed in Iraq I would have been killed. There is no freedom in Iraq."
Like Manar's husband, he hopes to one day be able to bring the rest of his family to safety in Europe, but in the meantime, he is ashamed at the depths he has had to sink to while staying on Kos.
"None of us would have ever imagined we would live like this in Europe," he says. "This is the first time in my life I sleep in the street, I feel bad that people pass by and see me sleeping in the street".
Hassan, too, has found the situation in Greece tough to deal with. The 22-year-old left his native Pakistan to find work overseas.
"It is difficult in Kos. I arrived 10 days ago and I am sleeping on the floor, with no electricity, food or water."
Like most of the migrants and refugees arriving on the island, Hassan does not intend to stay on Kos -- it is just the latest step on his journey to what he hopes will be a better life.
"I want to go to Italy and find a job; there are no jobs in my country," he explains. "When I make enough money in Italy I'll go back to my family."
Everyone on Kos says they feel pity for the migrants, insisting it is system, and not the people who are the problem: they just want to collect the papers allowing them to move on, but the process is slow, since the island does not have the resources to deal with an influx on this scale.
"There are 7,000 migrants on the island, we are only [about] 35,000 people here in Kos," says car rental agent Lia Passanikolaki. "We don't have enough police on the island to control the situation and process all these people.
"It is not a nice situation for them, it is not a nice situation for us, it is not a situation for anyone".
Last week, Kos's mayor, Yiorgos Kiritsis, called on the European Union to provide emergency financial aid to Greece to help it handle the influx.
The Greek government has tried to alleviate the crisis by sending a cruise ship to Kos, on which all new arrivals will be temporarily housed until they can be registered and move on.
"The ship will cover basic accommodation needs; identification will take place (on board), and the difficult situation on the island will be to a large extent alleviated," explained Alekos Flambouraris, Greek minister for the coordination of government work.
Greek authorities say the ship can shelter 2,500 people; but after just a day in the harbour, it is already home to more than 1,000 migrants.
And with up to hundreds of new arrivals landing on the island's shores every night, it is unclear how much this solution will do to ease Kos's ongoing crisis.