Japan retracts mistaken magnitude 9.9 quake alert

Japan's weather agency withdrew an erroneous alert for a magnitude 9.9 earthquake minutes after issuing it, apologising for the warning that disrupted transport.

The Japan Meteorological Agency (JMA) had initially warned on Friday that a magnitude 9.9 earthquake occurred near the Kuril Islands, known in Japan as the Chishima Islands, setting off loud emergency alerts on millions of mobile phones.

The JMA clarified later that a 6.9-magnitude quake occurred near Russia's Kamchatka Peninsula at a depth of 160 kilometres (100 miles) just after midday.

"We deeply apologise for the significant inconvenience and concern caused to the public," JMA official Shinya Tsukada told reporters.

The alert did not cause widespread panic, but briefly disrupted public transport.

According to the JMA, the error stemmed from an anomaly in calculating the earthquake's epicentre.

The estimated magnitude was based on an incorrect assumption that the epicentre was about 680 kilometres farther from Japan than it actually was, the weather agency said.

Japan is haunted by the memory of a massive 9.0-magnitude undersea quake in 2011, which triggered a tsunami that killed or left missing around 18,500 people and wrecked the Fukushima nuclear plant.

A 9.9-magnitude tremor would have released about 22 times as much energy as the 2011 quake, according to local media.