Thomson was not in the building at the time. Murdoch's whereabouts are unknown. The 11th floor was evacuated, as was the ninth floor where the mailroom is located.
The building is on Liberty Street in lower Manhattan, close to the Ground Zero site where the World Trade Center stood before it was attacked and destroyed on Sept. 11, 2001.
A News Corp spokeswoman was not immediately available for comment. News Corp's headquarters is in Midtown Manhattan.
The envelopes bore a Knoxville, Tennessee, return address, Brown said. It is unknown what the postmark says on the envelopes or whether they contained notes.
The incident follows others late last year in which powder was sent to media outlets and financial institutions.
In October, letters, many containing white powder, were sent to Chase bank offices and two other financial institutions in several states. They also were sent to The New York Times headquarters in New York and to Thomson Reuters Corp's Reuters newsroom in New York.
The letters sent to the financial institutions warned "it's payback time," according to a text released by the FBI in October.
- AP and Reuters contributed to this report.