on duty; while on official business
Used for public officials, civil servants, or employees when they are engaged in official duties. Often appears in formal contexts or news reports.
公務中の警察官が事故に遭った。
A police officer on duty was involved in an accident.
公務中は私用電話を控えてください。
Please refrain from personal calls while on official duty.
Compound of 公務 (こうむ, 'official duties') + 中 (ちゅう, 'in the middle of'). The reading is standard on'yomi.