紧急(jǐn jí) - urgent, pressing; emergency in Mandarin

紧急 (jǐn jí) describes a situation that will not wait: an emergency, a crisis, a deadline about to bite. It is formal in flavour and turns up on signs and in announcements as much as in speech.

Learn the fixed pairings, because that is where you will meet it: 紧急情况 (emergency), 紧急出口 (emergency exit), 紧急会议 (emergency meeting), 紧急通知 (urgent notice). In these it works as a noun modifier and 的 is normally dropped.

Do not mix it up with 紧张 (jǐn zhāng), which shares the first character but means nervous or tense as a feeling. 情况很紧急 is the situation is urgent; 我很紧张 is I am nervous. For the everyday "hurry up", 赶紧 (gǎn jǐn) is the natural choice.