Translation guide
The English adverb 'rapidly' describes an action happening at high speed or in a short time. In Japanese, this is most naturally expressed with adverbs like 速く (hayaku) or 急速に (kyūsoku ni), but the best choice depends on whether you're describing physical speed, quick change, or a fast pace of activity. Sometimes, the idea of 'rapidly' is built into the verb itself.
Describing movement or action that is fast in speed.
The most common and versatile adverb for 'fast' or 'quickly' in physical actions. Used with verbs of motion or action.
彼は速く走った。
He ran rapidly.
もっと速く歩いてください。
Please walk more rapidly.
Implies quick, agile, or nimble movement. Often used for reflexes or deft actions.
猫は素早く動いた。
The cat moved rapidly.
Means 'in a hurry' or 'hurriedly'. Focuses on the urgency rather than just speed.
彼は急いで家を出た。
He left the house rapidly.
Describing a situation, number, or state that changes quickly over time.
Formal adverb for rapid change, often used in news or business contexts. Implies a steep or sudden shift.
人口が急速に増加している。
The population is increasing rapidly.
状況が急速に悪化した。
The situation deteriorated rapidly.
Means 'suddenly' or 'abruptly'. Often used for unexpected rapid changes.
空が急に暗くなった。
The sky rapidly grew dark.
Onomatopoeic adverb suggesting steady, vigorous progress or increase. Casual and emphatic.
Describing work, speech, or processes done at a fast rate.
Literally 'at a fast pace'. A natural way to say something is done rapidly.
彼は速いペースで仕事を片付けた。
He finished the work rapidly.
Onomatopoeic adverb for doing things briskly and efficiently, without wasting time.
彼女はてきぱきと指示を出した。
She gave instructions rapidly and efficiently.
Specifically for speaking rapidly. 'In a fast-mouthed manner'.
彼は早口で説明した。
He explained rapidly (in fast speech).
速く (hayaku) is for physical speed. 急速に (kyūsoku ni) is for abstract or quantitative rapid change (formal). 急に (kyū ni) is for sudden, often unexpected changes (can be negative).
車が速く走っている。
The car is going rapidly.
需要が急速に伸びている。
Demand is growing rapidly.
急に雨が降り出した。
It suddenly started raining rapidly.
急速に is formal and often used in written Japanese or news reports. In everyday conversation, 速く or どんどん are more natural for most 'rapidly' situations.
新しい店がどんどんできている。
New shops are opening rapidly one after another.