A woman poses in front of a board during an event marking one year before the start of the Tokyo 2020 Olympic Games in Tokyo on Wednesday. Photo: VCG

Tokyo promised a high-tech Olympics complete with robots as it marked a year to go until the 2020 Games on Wednesday, hoping to leave behind some bumps in the road including an ongoing corruption investigation.

Organizers have battled everything from fears over deadly heat to persistent questions about the cost of the Games and how Tokyo won its bid.

But as the one-year countdown began, they touted speedy progress on venue construction and pledged a historic Games.

"I can truly say I have never seen an Olympic city as prepared as Tokyo, with one year to go before the Olympic games," said International Olympic Committee chief Thomas Bach at a ceremony Wednesday.

"All the elements that make a truly outstanding Olympic Games are in place," he added, predicting "an amazing experience" for athletes.

Officials pointed to "unprecedented" ticket sales and applications by 200,000 people for just 80,000 volunteer positions as evidence of building excitement for the Games.

"The six years since Tokyo was picked have zipped by, but I'm glad that ­preparations have gone very smoothly," ­Japan's Prime Minister Shinzo Abe said, before the symbolic handing-out of ­invitations to national Olympic committees.

Tokyo 2020 President Yoshiro Mori said Bach praised the speed of the city's preparations as "an Olympic record."

Half of the new permanent venues have been completed, and organizers say construction of the rest is on track.

While cooler weather this summer has assuaged fears raised by a deadly heat wave last year, organizers say they have a raft of safety measures planned in case temperatures soar.

Tactics from misting towers to ­flower beds - which don't radiate heat, and which organizers say also have a "psychological" cooling effect - will be tested this week at a beach volleyball event.

With the countdown under way, organizers have also been stepping up efforts to promote the Games as a showcase for Japan's high-tech know-how.

Japan's reputation as an industrial innovator has flagged since the last time it hosted the Games, in Tokyo in 1964, when it wowed the world with bullet trains.

But government and businesses are hoping to dazzle visitors with everything from driverless airport transport to robot greeters and mascots.

The organizers have even teamed up with two Japanese astronauts who will send messages of support from the International Space Station to those carrying the Olympic torch through the country.

The torch relay, featuring a rose-gold cherry blossom-shaped torch, will start from a sports center in Fukushima that housed workers battling to remove ­radioactive waste after the 2011 tsunami.

It will pass through other areas of northeast Japan devastated by the disaster, with authorities hoping to demonstrate the region's recovery.

Organizers also want the Games to be the "most sustainable ever" and are making everything from medals to podiums from recycled materials.