NEW YORK (AP) Police evacuated the newsroom and executive offices of the Wall Street Journal on Wednesday after about a dozen envelopes that contained a white powder were received.

At least four of the envelopes were opened; others were left unopened in the mailroom, police said.

About 250 employees were evacuated. Five employees were being decontaminated as a precaution, said FBI spokesman James Margolin.

A newspaper spokeswoman said the mail was addressed to several executives. The postmark was Knoxville, Tenn., but each letter had a different return address.

Authorities were trying to determine the nature of the powder.

The envelopes were found in three locations inside the lower Manhattan building, Margolin said. The 11th floor is shared by newspaper executives and editorial page employees. The 9th floor houses the newsroom and mailroom.

The Journal is published by Dow Jones & Co., a division of the media and entertainment company News Corp.

Employees who weren't needed immediately to put out the Journal or other Dow Jones publications were sent home.

Other staff members were working on two unaffected floors and at the nearby Marriott World Financial Center.

The Department of Homeland Security was monitoring the situation but said other agencies were taking the lead.

Associated Press writers Matt Apuzzo and Devlin Barrett in Washington contributed to this report.

Copyright 2009 The Associated Press.