A test emergency alert from Monterey Park's Emergency Operations Center was accidentally sent to mobile devices across Los Angeles County Wednesday afternoon, according to David Sommers, a spokesman for L.A. County Board of Supervisors.

The wireless emergency alert is part of FEMA's Integrated Public Alert & Warning System, which requires a monthly internal test, a FEMA spokesperson told KPCC, though that test didn't remain internal.

RELATED: Monterey Park emergency alert: False alarm reveals flaw in system

Sommers told KPCC that the test text message went out to a larger audience than anticipated, and Monterey Park city officials are working to fix the emergency alert system.

Tweet from Monterey Park FD

Wednesday's test alert transmitted screeching sounds to hundreds of mobile devices — and Angelenos immediately took to social media to express concerns.

Tweet about EOC alert

According to the San Gabriel Valley Tribune, Monterey Park unveiled its new 2,000 sq. ft. Emergency Operations Center (EOC) in July 2013. Funded by a federal grant, it cost approximately $500,000.

The Journal writes:

The new 2,000 sq. ft. facility will also be used for training and emergency exercises.

Besides having state of the art communications equipment, the facility is powered by a 100 kilowatt back-up generator and supplies to support a staff in an emergency situation.

KPCC has reached out to the city of Monterey Park but was unable to obtain details before this was published.

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Here's what folks on Twitter had to say about the unexpected alert.

Twitter reacts

This story has been updated.