kuài mǎ jiā biān
快马加鞭 (快馬加鞭)
to whip a galloping horse
to work at breakneck speed; pull out all the stops; to go as fast as possible
Example:
这项工作必须快马加鞭地进行。
Zhè xiàng gōngzuò bìxū kuài mǎ jiā biān de jìnxíng.
This work must be carried out at top speed