The 副詞（ふくし） (adverb)
直（ただ）ちに is commonly used in Japanese to convey that something is happening ‘immediately’, or ‘at once’. Like many adverbs, it will regularly appear at the beginning of a sentence.
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直（ただ）ちに避難所（ひなんじょ）へ向（む）かってください。
Please head to the evacuation point immediately.
この山（やま）から、 直（ただ）ちに出（で）て行（い）ってください。ここは私有地（しゆうち）です。
Please leave this mountain at once. This is private property.
地震（じしん）が起（お）きたら 直（ただ）ちに家（いえ）を出（で）てください。
If an earthquake occurs, please leave the house immediately.
Coming from the kanji 直（じき）, meaning ‘direct’,
直（ただ）ちに often carries the nuance that something is done ‘directly’ (and purposely). This is usually after something happens, or after something is completed. To indicate things that happen immediately, but not intentionally, 忽（たちま）ち may be used.
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計画（けいかく）が変（か）わったら、 直（ただ）ちに報告（ほうこく）してください。 (Intentional)
If the plan changes, please notify me immediately.
このファッションは忽（たちま）ち世界（せかい）で広（ひろ）まった。 (Unintentional)
This fashion spread around the world immediately.