外防輸入，內防反彈 [－－输－－内－－弹]

Jyutping ngoi6 fong4 syu1 jap6 ， noi6 fong4 faan2 daan2
Pinyin wài fáng shū rù ， nèi fáng fǎn tán

Definitions (Wiktionary)
  1. phrase, neologism
    to prevent both the importation and domestic growth of (COVID-19) cases