Bullet train services in eastern and central Japan resumed Wednesday, some 20 hours after a power outage caused hundreds of the shinkansen services to and from Tokyo to be canceled the previous day, affecting some 120,000 people.

All but two bullet train services on the Tohoku, Joetsu and Hokuriku lines have been operating normally since the morning, East Japan Railway Co. said.

The company completed restoration work shortly past 4:30 a.m., having removed a shinkansen train that lost power at around 10 a.m. Tuesday while running in Saitama Prefecture, where a slackened overhead electrical wire was hanging close to the rails.

JR East said it suspected the power supply was severed after pantographs on the running train clipped the loose cable, which likely slackened due to damage to a tension weight that had been in use for 38 years.

Photo taken at a ticket gate of JR Sendai Station in Sendai, Miyagi Prefecture, on the morning of Jan. 24, 2024, shows a notice saying that shinkansen bullet train operations are to resume from the first scheduled trains of the day. (Kyodo)

The company said it is investigating how the damage to the weight occurred and plans to conduct emergency visual inspections at around 500 locations where the same weights are used by Jan. 31.

It also said the section of the electric wire where the tension was lost had not been replaced with an updated version, designed to be more durable and easier to service.

"We don't know if the incident could have been prevented if the electric wire had been replaced with a new one," a company official said.

After Tuesday's incident, three other shinkansen traveling in the area also came to a halt around the same time but managed to move to Ueno Station in Tokyo.

The incident resulted in cancellations for about 280 bullet trains covering areas between Tokyo and other cities such as Sendai, Fukushima, Niigata and Nagano, according to the company. It also caused widespread disruptions for routes connecting to the capital.

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