With just six months to go before the 2025 World Exposition in the city of Osaka, there are still a host of challenges for organizers such as the slow sale of advance tickets.

The Osaka Expo is scheduled to take place on Yumeshima, an artificial island, from April 13 through Oct. 13 next year.

A ring-shaped roof with a circumference of around 2 kilometers — one of the world's largest wooden structures, now regarded as a symbol of the expo — has been completed, while the construction of foreign pavilions, which had been slow, has entered its final stages.