The officials' government email accounts were not vulnerable to the hacking because they were on more secure systems, NBC said.
A National Security Agency briefing in 2014 showed the email intrusion was detected in April 2010 and the U.S. official, who was not identified, said it was still going on, NBC said.
The official was cited as saying all top national security and trade officials were targeted.
Google acknowledged an intrusion into the private Gmail accounts of some American officials in 2011, and the NSA briefing made clear that email accounts from other providers also were compromised.
The hacking coincides with Hillary Clinton's use of a private email account as secretary of state from 2009 to 2013.
The targeted officials were not publicly identified.
U.S. officials code-named the email intrusion "Dancing Panda" and then "Legion Amethyst," according to NBC.