Clue: Clear area in emergency, initially — very critical (8)
Answer: EVACUATE
Explanation: Definition: Clear
 A(abbrev. for "area") **contained in**(in) [ **1st letter of**(…, initially) "emergency" + V(abbrev. for "very") + ACUTE(critical/at a point near a severe or disastrous outcome) ].
Defn: …/to empty.