The head of a Japanese sightseeing boat company whose vessel capsized in frigid waters in 2022 killing at least 20 tourists and crew has been arrested, the coastguard announced Wednesday.

The accident happened off Japan's northern Hokkaido island, and an additional six people are still listed officially as missing.

The Kazu I was carrying 24 passengers and two crew when it sent a distress signal off the coast of the Shiretoko Peninsula, prompting a search-and-rescue operation.

Authorities say the absence of any survivors made for an "extremely difficult, painstaking" investigation that took more than two years to complete.

But on Wednesday, Seiichi Katsurada, president of the Kazu I's operating company, was arrested on charges including professional negligence resulting in death, a coastguard official told reporters.

"Despite his responsibility in overseeing the cruise, the suspect was remiss in his duty to ensure the safety of passengers and crew, which caused this accident," the official said.

The boat set out on a sightseeing cruise to Shiretoko Peninsula, a designated UNESCO World Heritage site for its pristine natural environment and diverse wildlife.

A report by a government transport committee concluded last year that the Kazu I set sail without a deck hatch properly fastened, causing water to seep in.

The report also cited poor maintenance and oversight of the worn-out hatch, adding that the operator's lack of personnel with "sufficient expertise and experience in safe cruising" contributed to the disaster.

AFP

A crane lifts the salvaged Kazu I at Abashiri Port on June 1, 2022 © STR / JIJI PRESS/AFP/File

Japan company chief arrested for deadly 2022 boat accident