The 20th Asian Games were declared open by Japan's emperor on Saturday following a troubled build-up to the multi-sport spectacular that has more athletes than the Olympics.

There were a large number of empty seats at the 30,000-capacity stadium in Nagoya, where a subdued crowd saw a colourful opening ceremony on a heart-shaped stage.

Japan's Emperor and Empress were given a respectful reception as they took their seats alongside International Olympic Committee president Kirsty Coventry.

There was polite applause when Emperor Naruhito declared the Games open.

The first gold medal will be won on Sunday morning, likely in the men's individual triathlon, as the continent's finest athletes compete in more than 40 sports before the curtain comes down on October 4.

The event in Nagoya and Aichi prefecture has 2028 Olympics places up for grabs in seven sports and will be graced by global stars and fast-rising prodigies.

But it has been dogged by a series of problems as more than 11,000 athletes and 6,000 officials stretched organisers to the limit as they tried to accommodate all.

To save money there is no traditional athletes' village, competitors instead staying in a combination of temporary container-style huts, hotels and cruise ship the Costa Serena.

There was a record deluge last week which flooded parts of Nagoya and now a typhoon is approaching eastern Japan threatening further disruption in the coming days.

Some athletes were left stranded at the airport when transport failed to turn up and several teams have complained about the quality of the huts, including the beds being too short.

In the latest mishap, North Korea's national anthem was played on Friday for South Korea's men's hockey team.

- Cheers, empty seats - 

Two-time Asian Games silver medallist Zahra Kiani was a flag-bearer for Iran and hopes to win another medal in the Chinese martial art of wushu -- by watching how it's done on YouTube.

"I have been training with movies. I watch videos of Chinese athletes and I try to copy them," she said.

The Olympic Council of Asia said the continent's premier sporting event, featuring 45 countries and territories, had found the perfect host.

"When the world has needed it most, Japan has always answered," OCA president Sheikh Joaan bin Hamad Al-Thani said, referring to the Covid-delayed Tokyo Olympics in 2021.

He called those Games "a remarkable showcase of resilience, hospitality and commitment". 

Apart from Japan's athletes, the biggest cheer was reserved for China's competitors as they filed into the arena.

China will again expect to top the medals table after winning a whopping 201 golds and 383 medals on home soil in Hangzhou last time.

- Prodigies in spotlight  -

As always at the Asian Games -- which started in 1951 -- Olympic staples such as athletics and swimming will sit side-by-side with regional favourites like sepak takraw and kabaddi.

There will be eSports, breakdancing and BMX cycling. Padel and MMA will make their Asian Games debuts.

Among those competing will be Philippine tennis sensation Alexandra Eala and a pair of prodigies in 15-year-old Indian cricketer Vaibhav Sooryavanshi and 13-year-old Chinese swimmer Yu Zidi.

Taiwan boxer Lin Yu-ting will also be competing, two years after she won Paris Olympics gold in the middle of a major gender row that saw her eligibility questioned.

North Korea will have more than 100 athletes competing across 14 sports, aiming to "bring joy to Marshal Kim Jong Un".

Sooryavanshi will be part of an India cricket team looking to make a statement before the sport returns to the Olympics in Los Angeles after an absence of 128 years.

India could face bitter rivals Pakistan in the final at Nagoya's new purpose-built cricket ground -- if rain does not intervene.