Oftentimes you will have to say you are in the middle of doing something and there are a few ways to do that in Korean. One of the ways how you can say some action or event is under way is by using the Korean time expression 중.
중 is one of the Korean grammar topics that is based around Hanja, like 후에 and 전에. The character, on which it is based is, 中 [중], which means ‘middle’. It clearly gives away the purpose of this specific grammar topic. The purpose of 중 is to indicate an event, state or action is in the middle of happening. In this regard it is nearly identical to the Korean progressive tense, -고 있다. However, there is a slight difference between the two.
-는 중 vs. -고 있다
While both -는 중 and -고 있다 indicate an action is currently taking place, there is a major difference between the two. You can use the latter when the subject in the sentence is natural phenomena like rain. However, you cannot use the former in that case. Keep this limitation in mind.
비가 오고 있어요. (Correct)
비 오는 중 있어요. (Incorrect, you need to use -고 있다 with the natural phenomenon 비, rain)
가: 왜 여기에는 너무 시끄러워요?
나: 우리 집 옆에서 섬성 사옥 공사 중이에요.
A: Why is it too noisy here?
B: They are building a Samsung office next to our house.
How To Use
Using the Korean time expression 중 is pretty simple once you understand it is technically nothing more than a noun itself. Therefore, when you use it with another noun, you simply put the noun before it and you are done. With verbs, you simply need to turn it into a present tense noun phrase. To do that you simply need to attach -는 to the verb stem and you are done. Just keep Korean irregular verbs in mind like the ㄹ irregular verbs. Remember that you can either use the noun or a noun phrase when the verb is a 하다 verb.