Revealed: How Tokyo is preparing in case a massive earthquake hits 2020 Olympics

It's 9:15 am on Sunday July 26 and excitement is building at the Tokyo Aquatics centre as the first swimming medals are up for grabs. Nearby at the Ariake Gymnastics Centre, US superstar Simone Biles is warming up for her first appearance at the 2020 Olympics.

Without warning a 7.3-magnitude earthquake rips through Tokyo Bay, the ground shakes violently causing citywide damage, widespread panic and multiple casualties.

Fortunately, this is just an imagined scenario at a disaster drill carried out just before Christmas, as Tokyo 2020 organisers prepare for the worst, while hoping they will never have to do it for real.

At the gymnastics venue in Tokyo Bay the public address springs into action in Japanese and English.

"There has been an earthquake. Please stay calm and protect yourself. This venue is safe," the advice crackles. "Taking action in a panic may lead to danger. Please stay calm and follow the staff's instructions. The elevators may not be used."

Emergency first aid | Within minutes, blue uniformed officers from the Tokyo fire department in their white helmets stream into the stadium.

"Are you OK?" emergency first responders shout as they tend to bodies littering the stands. Officials urge calm via loudspeakers and console elderly spectators.

Fifteen minutes later, troops from the Japanese self-defence forces in military uniform burst into the venue and are briefed on the situation as the evacuation gathers pace.

Troops bring in white stretchers and carry the injured to a triage area hastily set up adjacent to the gymnastics mats. Medics perform emergency first aid on people laid out on red blankets as commanders bark out orders in a fevered but efficient atmosphere, sending less urgent cases to another venue.

Dozens of spectators, including the walking wounded and those in wheelchairs, are evacuated through the wide boulevards of the Tokyo Bay area, but efforts are hampered by a 6.0-magnitude aftershock at 10:30am.

Across town, at the imposing Tokyo Metropolitan Government building, city governor Yuriko Koike convenes an emergency gathering with 40 of her top officials from the city authorities, fire department, coastguard and self-defence forces.

She receives a briefing on the evolving situation in her quake-hit city, with a dozen monitors showing still images of the damage at the gymnastics venue and the location of fires burning around Tokyo.

Koike orders that all resources be diverted to saving lives but that infrastructure such as port and river facilities must also be inspected and repaired if necessary.

"We have many guests domestically and from abroad for the Tokyo 2020 Games," she says, wrapping up the meeting. "Please exert your utmost efforts to ensure the safety of spectators and Games workers as much as you do for Tokyo residents," she orders.

The large-scale drill, over two locations and involving more than 500 volunteers, is part of Tokyo 2020's contingency planning as they gear up to host the Games in one of the world's most seismically active countries.

Typhoons and terror | Sports fans already had a taste of Japan's vulnerability to natural disasters when a powerful typhoon struck during the Rugby World Cup, forcing the unprecedented cancellation of three matches.

While July and August, when the Olympics are held, is not peak typhoon season, they can strike at any time - as can earthquakes or terrorist attacks - and organisers want to be as prepared as possible.

Tokyo firefighters included an anti-terrorism drill alongside emergency preparations in their traditional new year display. While visitors from around the world may be unnerved by earthquakes, officials stress there is no country better prepared or equipped.

Japan experiences thousands of tremors per year of varying sizes and the vast majority cause little or no damage, with emergency services well drilled.

Paralympic boss Andrew Parsons recalled in a recent AFP interview being in a Tokyo hotel when a medium-sized earthquake shook his room and he rushed to reception in a mild panic. "I was the only one who seemed to notice," he laughed, amused by the blase response of local residents.