Japan's prime minister urged the importance of unity in a world plagued by "divisions" at a futuristic but also tradition-steeped opening ceremony for the World Expo on Saturday.
Everything from a Mars meteorite to a beating heart grown from stem cells will be showcased during the six-month event, which opens to the public on Sunday.
The vast waterfront site in Osaka will host more than 160 countries, regions and organizations.
"Having overcome the Covid pandemic, the world now faces the crisis over many different divisions," Japanese Prime Minister Shigeru Ishiba told the opening ceremony.
"It is extremely significant that people from all over the world gather and face the question of life in this era, exposing ourselves to state-of-the-art technology and diverse cultures and ways of thinking," Ishiba said.
Expo is also known as a World's Fair and the phenomenon, which brought the Eiffel Tower to Paris, began with London's 1851 Crystal Palace exhibition and is held every five years.
Most pavilions -- each more outlandishly designed than the last -- are encircled by the world's largest wooden architectural structure, a towering latticed "Grand Ring" designed as a symbol of unity.
An array of colorful imagery symbolizing life, birth and nature adorned a massive screen in a minutes-long video at Saturday's ceremony, with foreign dignitaries and Japan's royal family in attendance.
The ceremony displayed a mix of technology, including its AI-powered "virtual human" master of ceremonies, and tradition that included Japanese kabuki dancing and taiko drums.
Emperor Naruhito said he hopes Expo 2025 will "serve as an opportunity for people worldwide to respect the lives not only of their own but also of others".
Heightened security was put to the test hours before the ceremony when a suspicious box was found at the nearby Kyoto train station and reported to police.
A bomb squad was sent to the scene, causing train delays, but it was found that the box only contained "foreign-made sweets", according to Japanese media.
Osaka last hosted the Expo in 1970, when Japan was booming and its technology was the envy of the world. It attracted 64 million people, a record until Shanghai in 2010.
However, Expos have been criticized for their temporary nature, and Osaka's man-made island will be cleared to make way for a casino resort after October.
Only 12.5 percent of the Grand Ring will be reused, according to Japanese media.
Opinion polls also show low levels of enthusiasm for the Expo among the public.
So far 8.7 million advance tickets have been sold, below the pre-sales target of 14 million.
Japan is also experiencing a record tourism boom, meaning accommodation in Osaka -- near hotspot Kyoto, and home to the Universal Studios Japan theme park -- is often fully booked with sky-high prices.
