A great number of the stranded people are living at the makeshift border camps in very poor conditions.
Many of them are exposed under rainy and freezing weather with very little protection, and they're seriously short of food, water and basic supplies.
Insufficient sanitary facilities have also posed a threat that illness and disease could spread.
Cristian Reynders, deputy coordinator for Doctors without Borders, believes that the poor living conditions have already resulted in a whole range of illnesses especially among young children.
"We see in our consultation like in four days we have three (hundred) to 750 patients, out of which more than 120 were under five (years of age) children. Their respiratory infection are pretty worrying because they are exposed to these weather conditions, they are exposed to the lack of hygiene in the camp. They are suffering, we don't have exact numbers to be honest, but we know that children are sleeping outside, outdoors, yes."
Cecile Van de Kontinenburg, also with Doctors without Borders, expressed her concerns about these younger residents.
"You can clearly see that the living conditions are affecting the health of the children. When it's raining and they don't have shelter, they will be cold, they will catch a cold, they will catch respiratory diseases. When the weather is cold you can see that the cold is really bothering them, we have had a lot of children with hypothermia as well because they didn't have enough shelter. The hygienic conditions when there's 12,000 people aren't optimal, so we see a lot of diarrhoreal diseases as well."
She also worried that there might not be enough time and supplies to meet people's basic needs.
Migrants have become stranded in Greece after a number of European countries along the Balkan migration corridor imposed border restrictions and limited the number able to cross.
The United Nations refugee agency said Macedonia has allowed only 187 migrants to enter its territory.
Describing the situation as "a huge humanitarian crisis", Central Macedonia Governor Apostolos Tzitzikostas has asked Greek authorities to declare a state of emergency.
"We're trying to do whatever we can as a regional government, along with the municipalities, in order to support the very, very important effort that the Red Cross and other NGOs are doing here in the area for the support of the refugees."
He also urged Macedonia to lift its border restrictions as soon as possible, and said that severe actions should be taken against the countries closing their borders.
For CRI, I'm Xie Cheng.
