中In progress or during
Attach 中 to an activity, process, status, or compatible period noun to say that it is in progress, or that something happens during it.
Attach it directly to the noun
Do not insert の between the noun and 中. The noun normally names an activity, process, status, or recognizable period. The resulting expression treats that activity or period as currently underway or as the time within which something occurs.
The main sentence patterns
Choose the following particle by its job
中だ describes what is in progress. Use 中に when a particular event occurs within that period. Use 中は when describing a situation, arrangement, or rule that continues during the period. These are tendencies based on meaning, not automatic translations of English prepositions.
In progress versus the whole range
In the first example, 中 places an event inside an ongoing activity. In the second, 中 covers the whole day. The written character is identical, so meaning and the noun before it determine the reading.
More examples
授業中に地震がありました。
There was an earthquake during class.
Analyze入院中は毎日、本を読んでいました。
While I was in the hospital, I read books every day.
Analyzeただいま申込受付中です。
Applications are now being accepted.
Analyze旅行中の写真を家族に見せました。
I showed my family photos from the trip.
Analyzeただいま準備中ですので、少々お待ちください。
We are currently preparing, so please wait a moment.
Analyze昼休み中に銀行へ行きました。
I went to the bank during my lunch break.
Analyzeこの機械は修理中なので、使えません。
This machine is being repaired, so it cannot be used.
Analyze