甕中捉鱉 [瓮－－鳖]

Jyutping ung3 zung1 zuk3 bit3
Pinyin wèng zhōng zhuō biē

Definitions (CC-CEDICT)
  1. lit. to catch a turtle in a jar (idiom)
  2. fig. to catch sth that has no way to escape
Definitions (Wiktionary)
  1. phrase, idiomatic
    to catch or arrest a target already within one's grasp (and cannot escape)