It came without warning. As workers were busy preparing forecasts and alerts at a National Weather Service center in Maryland on Wednesday morning, they were suddenly interrupted by a message in Chinese piped over the building’s intercom.

The voice was a woman’s, which also reached building employees via phone at the National Oceanic and Atmospheric Administration’s Center for Weather and Climate Prediction in College Park, Md.

On Wednesday afternoon, Weather Service officials scrambled to understand the source of the audio intrusion.

“We are aware of the Chinese message that is propagating through the phone system and was [broadcast] over the building PA,” read an email from Doug Fenderson, the branch chief for infrastructure and Web services at the center, sent at 12:50 p.m. “We are engaging the Vendor AT&T to alert them of the incident and get root cause. The phone [system] is not tied to any of the Government IT controlled systems in the building. Please do not be alarmed.”