A hacker group based in Russia has attacked the Port of Nagoya, Japan's largest port by total cargo throughput and responsible for handling some of Toyota Motor Corp.'s exports and imports, the operator of the port's computer system said Wednesday.

The group, LockBit 3.0, has made a ransom demand in exchange for the system's recovery, Nagoya Harbor Transportation Association said, while police have launched an investigation.

The port in the central Japan prefecture of Aichi has remained unable to load and unload containers from trailers, its operator Nagoya Port Authority said, adding it intends to resume operations Thursday morning.

Photo taken on July 5, 2023, shows container terminal of Port of Nagoya in Aichi Prefecture. (Kyodo)

The system failure occurred at around 6:30 a.m. Tuesday when an employee was unable to start a computer, according to the port authority.

A message indicating that the computer system had been infected with ransomware was somehow sent to a printer, a source familiar with the case said.

Ransomware is malware that encrypts data and demands payment in exchange for restoring access.

The port is a hub of Toyota's exports and imports. The carmaker said that it cannot load or unload auto parts due to the glitch.

But the company added that there has been no disruption to its production so far, and the logistics of finished vehicles remain unaffected because it is managed using a different computer system.

"We will closely monitor any impact on production while carefully examining the parts inventory," Toyota said.

Its suppliers, including Denso Corp., Aisin Corp. and Toyota Industries Corp., have also secured a certain amount of inventory and will only have limited exposure to the system failure, Toyota said.

The port has remained Japan's largest since 2002. Its cargo throughput in 2021 reached 177.79 million tons, according to the operator.

Temporary congestion of trailers was observed at the port.

"If these many trailers resume operation all at once, it would be very crowded. It seems tough even after the system recovers," a trailer driver in his 30s said.