Loud alarms rang from cellphones and TVs just before 5 p.m. on Thursday warning of a magnitude-7.8 quake, which could cause severe damage. It said residents throughout Japan should be prepared.
A few minutes later the Meteorological Agency reported a magnitude-2.3 quake centered in Wakayama prefecture in western Japan. Under the Japanese system for measuring quakes, it barely registered.
Public broadcaster NHK said the agency blamed electronic noise for triggering the apparently false alarm.
The alert caused a brief halt of high-speed train services.
Japan beefed up its warning systems following a magnitude-9 earthquake and tsunami in March 2011 that killed more than 18,000 people. That disaster raised concern over Japan's level of readiness for such catastrophes.
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