Alvaro Martin of Spain captured gold in the 20-kilometre race walk in the opening event of the World Athletics Championships on Saturday.

Martin moved into the lead with about 5km remaining to finish in one hour 17.32 seconds, the fastest time in the world this season, on the soggy 1km loop course that started and finished at picturesque Heroes' Square.

Sweden's Perseus Karlstrom, a three-time world bronze medallist, won silver in 1:17.39, while Caio Bonfim of Brazil claimed the bronze (1:17.47) to match his medal from the 2017 worlds in London.

Martin, who was fourth at the Tokyo Olympics and seventh at the worlds last year in Eugene, shaved nearly two seconds off his best time.

The 29-year-old clutched a Spanish flag down the home stretch, waving it in victory. He lapped defending champion Toshikazu Yamanishi of Japan on his approach to the finish line.

Martin missed the Spanish record by 10 seconds, but the next five walkers all set national records in a contest that had 18 men dip under the 1:20 mark in one race for the first time.

Athletes were almost on the starting line when a thunderstorm delayed the start of the race by two hours.

Japan's Koki Ikeda took the early lead and stretched the gap to 15 seconds before Martin passed him at 15km. Ikeda fell well off the pace to finish 15th.

There will be a 35km race walk on Thursday but Saturday's shorter event is the distance walkers will race at the 2024 Paris Olympics after the 50km event was contested for the last time at the 2020 Tokyo Games.