(Adds details on affected employees)

NEW YORK, Jan 21 (Reuters) - Three executives at News Corp's NWSA.O Dow Jones & Co headquarters received envelopes containing white powder on Wednesday and 10 more were discovered in the mailroom, prompting evacuations of two floors of the building.

The building contains Dow Jones as well as its Wall Street Journal daily business newspaper. The New York Police Department and New York Fire Department’s Hazmat teams are investigating.

Authorities do not yet know if the powder is dangerous.

The letters were sent to Wall Street Journal Managing Editor Robert Thomson, Dow Jones Chief Executive Les Hinton and Journal Editorial Page Editor Paul Gigot, according to a source familiar with the matter.

Five female employees were temporarily quarantined and later released, according to an employee memo. The employees are “apparently in good spirits and good health,” said the memo, written by Dow Jones human resources executive Gregory Giangrande.

U.S. authorities have been on alert for mail with white powder in it since 2001 when envelopes laced with anthrax were sent to media outlets and U.S. lawmakers, killing five people.

The envelopes were found on the 11th floor, where News Corp Chief Executive Rupert Murdoch and Thomson have offices, Wall Street Journal spokesman Robert Christie said.

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 NYT.N headquarters in New York and to Thomson Reuters Corp's TRI.TOTRIL.L 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.

“We have had many of these in the last year and they typically are talcum powder or cornstarch,” New York Police Department spokesman Paul Browne said. (Additional reporting by Christine Kearney; Editing by Andre Grenon and Maureen Bavdek)