The Japan Karate Federation on Thursday said eight of its athletes tested positive for the Omicron variant of the coronavirus after returning from the recent Asian championships in Kazakhstan.

The eight were part of the 28-member Japanese team which contested the Dec. 18-22 tournament in Almaty, where athletes and team officials remained within an infection control bubble comprising sports venues and hotels.

The traveling party took PCR tests upon returning to Japan on Dec. 24, with 11 members -- 10 athletes and one official -- testing positive for the coronavirus.

Electron micrograph of the Omicron variant of the novel coronavirus. (File photo courtesy of the National Institute of Infectious Diseases)(Kyodo)

Eight among them were later confirmed as having the Omicron variant. According to health authorities, the three others may also have Omicron, although one of the 11 is no longer positive for the coronavirus.

Further tests on Dec. 25 revealed four new positives, but there was no indication of whether they were for the Omicron strain. Two further mild or asymptomatic cases have since emerged, bringing the total number of currently infected team members to 16.

Some 450 athletes, including juniors, from more than 20 countries and regions took part in the championships.

World Karate Federation general secretary Toshihisa Nagura, who visited the competition site, said measures to prevent infection "were thorough."