voluntary evacuation
Evacuation undertaken at one's own discretion, typically before an official order is issued, often in the context of natural disasters.
I decided to evacuate voluntarily before the typhoon approached.
The city is urging elderly residents to evacuate voluntarily.
避難 is a general term for evacuation, while 自主避難 specifically refers to evacuation done on one's own initiative, without waiting for an official order.
避難勧告 is an official evacuation advisory issued by authorities, whereas 自主避難 is a voluntary action taken by individuals before or in the absence of such an advisory.
Compound of 自主 (じしゅ, 'autonomy; self-determination') and 避難 (ひなん, 'evacuation; taking refuge').