Prime Minister Fumio Kishida called off a planned trip to Central Asia out of an abundance of caution following the warning. Bullet trains were running at reduced speeds, national broadcaster NHK is running cautionary graphics and some semiconductor-related factories temporarily halted production. Some beaches in the affected regions have been closed off for the time being, according to local reports. 

A megaquake in what’s known as the Nankai trough could surpass the damage from the March 2011 earthquake and tsunami that devastated the northern coast of the main island of Honshu. The zone, where the Philippine sea plate subducts underneath the Eurasian continental plate, sees a major tremor occurring in 100- to 150-year cycles.

The precautionary warning system for an increased risk of a quake, implemented in 2019, kicks in when a magnitude-6.8 or larger earthquake strikes an area where megathrusts are expected to occur, or when anomalous shifts in the plates are detected. Depending on the size of the earthquake at the time, the authorities can issue different levels of caution, and in some cases warn people to evacuate away from tsunami-prone areas for as long as a week. 

“This is advice to be prepared for the possibility that major earthquakes will continue,” Kishida told reporters in Nagasaki, where he was attending ceremonies for the 79th anniversary of its atomic bombing. “It’s not a warning to evacuate in advance, nor is it a notice that an earthquake will occur within a certain period, but it is the first time, so I think the people will be extremely uneasy.”

There were reports of several injuries and limited damage from the magnitude-7.1 earthquake that struck off the coast of Kyushu Thursday. The island is home to Sony Group Corp.’s semiconductor factories. Taiwan Semiconductor Manufacturing Co., which opened one factory there, is about to open a second one later this year and is considering a third. 

NHK broke into Olympics coverage to report the quake and the subsequent megaquake warning, and continued to issue bulletins on Friday. A 2019 analysis by a government panel estimated that more than 230,000 deaths could occur in the worst case scenario from a Nankai trough quake.

Big earthquakes have followed smaller tremors in the past. Foreshocks began two days prior to the 2011 9-magnitude earthquake, the most powerful recorded in Japan. Damage from the tremor and resulting tsunami killed almost 20,000 and triggered a meltdown and radiation leakage from a nuclear facility in Fukushima.

Central Japan Railway Co. said its bullet trains are running slower between Tokyo and western Japan until the warning lifts. Japan’s regulatory body said it issued alerts to all nuclear power plants in the nation to take precautions. Electronic component-maker Kyocera Corp. said some equipment was damaged at a plant in Kagoshima. 

Local governments and companies are responding after the Japan Meteorological Agency issued the advisory on Thursday. Stocks closed the day slightly up and the yen was little changed at around ¥147 to the dollar. 

Chipmaker Rohm Co. temporarily suspended operations in Miyazaki prefecture in Kyushu and said safety checks are under way according to a spokesperson. Sumco Corp., a maker of silicon wafers needed in chip-making, has halted operations at its plant in Miyazaki, according to a representative. 

Hiroaki Maruya, a professor at the International Research Institute of Disaster Science, said that companies may take the opportunity to brush off their business continuity plans following the alert, or go through disaster drills. 

“NHK has been reporting on this event, so they may make a move,” Maruya said.

Suntory Holdings Ltd., Suzuki Motor Corp. and other companies said they were making checks and were on alert for any further developments. 

Regional utility Kyushu Electric Power Co. said that it has set up a task force to organize communication with its power plants. A spokesperson for the company said that its nuclear power facilities — Genkai Nuclear Power Plant in Saga prefecture and Sendai Nuclear Power Plant in Kagoshima prefecture — are designed with a Nankai trough quake in consideration. 

Chubu Electric Power Co., a utility covering central Japan, said it has set up a network to strengthen communication between headquarters and branch offices, according to the spokesperson.