Relatives prayed for the victims of a 1985 Japan Airlines jumbo jet crash on Monday, the 34th anniversary of the world's deadliest single-aircraft accident.

A ceremony was held in the evening in the village of Ueno at the foot of the Osutaka Ridge in Gunma Prefecture, northwest of Tokyo, where the plane went down, killing 520.

The relatives offered silent prayers at 6:56 p.m., the time of the crash, after climbing the steep mountain trail to grave markers and a monument at the crash site to mourn their loved ones.

Concerns over air safety increased recently following a series of alcohol-related incidents at Japanese airlines including JAL, such as higher-than-permissible limits of alcohol detected in pre-flight tests for flight crew.

(File photo)

"People may think 'What is JAL doing? Did it forget the crash?'," Yuji Akasaka, president of Japan Airlines Co., told reports after offering flowers at the monument. "I felt guilty while I was climbing the mountain. We will strengthen our efforts to change our crew members' mindset."

JAL should "look back to the memories and lessons of the accident," said Masayoshi Yamamoto, 39, who lost his father Kenji at the age of 49 in the accident.

Toru Izutani, 60, said he came to the venue to tell his younger sister who died at the age of 20 that he has a grandchild born in May.

"I have lived the best I can for my sister," he said.

(Relatives of the jet crash victims pay tribute to their loved ones on Aug. 11, 2019.)

On Aug. 12, 1985, JAL flight 123, a packed Boeing 747 en route from Tokyo to Osaka during Japan's Bon summer holiday season, crashed about 40 minutes after taking off.

The crash claimed the lives of all but four of the 524 crew and passengers on board, many of whom were on their way home to see their families.

In 1987, a Japanese government investigation commission concluded that the accident was caused by improper repairs conducted by Boeing Co. on the plane's rear pressure bulkhead, whose rupture blew off the craft's vertical stabilizer and destroyed its hydraulics.