Tens of thousands of people flocked to South Korea's 2012 international expo Saturday on the first day of the three-month show with the theme of "The Living Ocean and Coast".

The southern coastal city of Yeosu opened Expo 2012 to the public after four years of preparation and $10 billion investment, with 104 participating nations showcasing their oceanic culture and science.

Ten international organisations and eight firms are also staging exhibitions at the 25-hectare (60-acre) seafront area, which features pavilions, a giant aquarium and a floating stage for performances.

Organisers said they expected a total of 10 million visitors by the end of the expo in August, including up to 800,000 foreigners, mostly from China and Japan.

"There's no rush... our goal is drawing genuine visitors by word of mouth, not trying to boost attendance with usual free tickets and other artificial measures," Cho Yong-Hwan, an organising committee spokesman, told reporters.

Expo 2012 Yeosu is being held between the headline World Expos, which are staged every five years. The last was in Shanghai in 2010.

Tourism in Yeosu -- home to 300,000 people -- has been limited due to poor transport links and outdated infrastructure despite a scenic coastline and hundreds of nearby islands.

The government has poured in billions of dollars to build new roads and railways since the port city won its expo bid in 2007.

Organisers predict the event will create some 80,000 jobs and bring economic benefits worth 19 trillion won ($17 billion) -- outweighing the massive spending.

On Saturday, the site, formerly a dusty cement terminal, was teeming with tourists -- mostly South Korean -- with long queues forming at major exhibitions by countries including the US, Japan and China.

Japan focused on the deadly quake-tsunami disaster that hit its northeastern coast last year, playing an animated film about people trying to rebuild their lives while protecting sea life.

The US exhibition featured a water screen display showing President Barack Obama expressing a commitment to protecting maritime ecosystems and resources.

Singapore showcased how the city state transformed itself into a lush green metropolis, displaying miniature versions of its urban gardens and its eco-friendly offshore landfill that is home to hundreds of animals and plants.

Australia, the world's largest island continent, played a live video from the Great Barrier Reef, allowing people to see underwater scenes of the world's biggest coral reef site and chat with divers.

"It's far smaller than the Shanghai expo in scale, but it's impressive enough," said Chinese tourist Jenny Gao, walking under a 218-metre-long (715-foot-long) gallery -- twice as long as a soccer pitch -- displaying LED images of the ocean.

Chinese visitors have snapped up more than half of the tickets on advance sale and organisers have filled some 1,000 of the 13,000 volunteer helper posts with Chinese living in South Korea to better serve them.

"More Chinese have become interested in expos since the Shanghai event... I will be happy to recommend my friends and parents to visit," Gao told AFP.