Prime Minister Shigeru Ishiba urged the importance of unity in a world plagued by "divisions" at a futuristic, but 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 pavilions of more than 160 countries, regions and organizations.