Norwich Cathedral was evacuated when a fire alarm went off just as the Norwich School's remembrance service was about to start.
Firefighters were called just after 10.30am today and an automated announcement urged people to leave the ancient building.
A fire crew from the Norwich Carrow base went to the cathedral and, by 11am, they had established that it was a false alarm.
The remembrance service will now go ahead at noon.
The names of more than a hundred Norwich School pupils who lost their lives in the first and second world wars will be read out.
Cathedral sacrist Roger Lee said the alarm was triggered due to a malfunction in a sensor.
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