One of the world's most prestigious sporting events, the World Athletics Championships, got underway in the Japanese capital, Toyko, on Saturday.

Tens of thousands of spectators gathered in the city's National Stadium to watch the final lap of the opening 35-km (28-mile) men's race walk ahead of the day's other competitions.

The championships, due to run till September 21, are taking place four years after Tokyo hosted the 2020 Olympics with a year's delay under pandemic conditions that meant fans were banned from venues to prevent the spread of COVID-19.

Return of controversial gender testing

Ahead of the event, the World Athletics federation reimposed an obligation on athletes wanting to compete in the female category to undergo a gene test to determine their sex.

It said on Friday that about 95% of female athletes set to compete in Tokyo had completed the SRY test, designed to detect a "Y" chromosome found in males, thus complying with a September 1 deadline.

Coe has defended the federation's policy,  saying the test fostered the "protection and the promotion of the integrity of women's sport."

The test is, however, considered an unreliable indicator of femaleness by many, as the "Y" chromosome can be present in females without giving them a male physiological advantage.

In a sign of how controversial the matter is, athletes from France were forced to have the text conducted at foreign training sites as their country has banned that kind of screening for nonmedical purposes.

For reasons of confidentiality, it is unclear whether any athletes have been ruled ineligible for women's events on the basis of the test.

Critics of the screening see it as a spillover from the ongoing "culture wars," with, in particular, many right-wing figures vigorously opposing any inclusion of transgender athletes identifying as female in women's sports.

'Largest sporting event of the year,' says Coe

Some 35,000 spectators were at the National Stadium on the opening day, meaning the venue was only half-full.

However, several other sessions are booked-out.

The race walk was won by Evan Dunfee of Canada, followed by Spain's defending champion Maria Perez.

Japanese fans were, however, delighted by the bronze success of their compatriot Hayato Katsuki, who entered the stadium to a huge roar from the crowd.

The rest of the day was devoted to field events including discus and shot put.

World Athletics President Sebastian Coe on Friday called the championships "the largest sporting event of the year by some distance."

Edited by: Jenipher Camino Gonzalez