Confronted with a plunge in its stock markets last year, China’s central bank swiftly reached out to the U.S. Federal Reserve, asking it to share its playbook for dealing with Wall Street’s “Black Monday” crash of 1987.

The request came in a July 27 email from a People's Bank of China official with a subject line: "Your urgent assistance is greatly appreciated!"

In a message to a senior Fed staffer, the PBOC's New York-based chief representative for the Americas, Song Xiangyan, pointed to the day's 8.5 percent drop in Chinese stocks and said "my governor would like to draw from your good experience."