HONOLULU (AP) — Honolulu officials accidentally set off the city’s emergency sirens about 20 minutes before a monthly test was due to take place.

The Hawaii Emergency Management Agency says the sirens mistakenly blared at 11:21 a.m.

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The city later set off the sirens again at 11:45 a.m. for the regularly scheduled monthly test. The error occurred only on Oahu.

Hawaii’s counties test their emergency sirens at 11:45 a.m. on the first working day of every month.