On duty; at work; during working hours. Used as a noun or adverbial phrase (e.g., '勤務中は〜').
勤務中は私語を控えてください。
Please refrain from private conversations while on duty.
彼は今勤務中で、電話に出られません。
He's on duty now and can't take the call.
医師が勤務中に緊急手術を行った。
The doctor performed an emergency surgery while on duty.