The time period overlaps with Hillary Clinton's use of a private email account while Secretary of State from Jan. 21, 2009 to Feb. 1, 2013. The names and ranks of the officials whose emails were actually grabbed, however, were not disclosed in the NSA briefing nor by the intelligence official.
A different NSA document leaked by Edward Snowden revealed that in late 2010 China had attempted to spy on the emails of four U.S. officials, including then Joint Chiefs of Staff Chairman Adm. Mike Mullen and Chief of Naval Operations Adm. Gary Roughead. The document, posted on-line by Der Spiegel earlier this year, said the Chinese spies had tried to insert malicious software into their computers.
Read MoreMicrosoft Outlook 'hacked' by Chinese authorities
NBC News reported in 2013 that prior to the 2008 presidential election, Chinese cyber spies had targeted the presidential campaigns of then Sen. Obama and Sen. John McCain in order to read emails and policy papers, and had successfully compromised some emails, including private correspondence from McCain.
The "Dancing Panda" campaign revealed in the 2014 NSA briefing paper was among more than 30 "intrusion sets" launched by China that the NSA and other intelligence units identified last year in classified documents. NBC News reported last week that those campaigns resulted in more than 600 successful attacks on targets.
The NSA declined to comment.