Democratic presidential candidate John Edwards' campaign headquarters in North Carolina was evacuated after a staff member opened a letter containing white powder, a campaign official said.

"The health and safety of our staff and volunteers is obviously our paramount concern, so we contacted the authorities," Jonathan Prince, deputy campaign manager said after the evacuation Wednesday. "The authorities have asked us to evacuate while they run tests on the substance, and we have done so."

Chapel Hill police spokeswoman Jane Cousins said the campaign worker who opened the legal-size envelope containing the powder has been interviewed by health officials and has shown no health problems.

Police contacted the regional hazardous materials response team, the FBI and the fire department, Cousins said. Hazardous materials experts were testing the substance, she said.

Campaign employees are working from home until investigators reopen the headquarters, campaign spokeswoman Kate Bedingfield.

White powder in letters has been associated with anthrax since an attack in 2001 killed five people and sickened 17.