TOKYO (Kyodo) -- Preparations for the 2025 world exposition have entered the final stretch with two months left until the event opens in Osaka, where delays in pavilion construction continue to pose a major challenge for the organizers.

The massive Grand Ring wooden roof structure has been completed, with contractors adding the final touches by placing plants along its promenade.

With over 28 million visitors expected during the event from April 13 to Oct. 13, a train station connecting to central Osaka was opened recently at the venue on the artificial island of Yumeshima that will handle up to 133,000 people each day.

For connecting bus services, another key means of transportation for visitors, a terminal to handle both shuttle and long-distance buses was also completed earlier this month.

In mid-January, participating countries held their final joint meeting in western Japan before the event's opening, with a dozen countries offering further details about their exhibits and the organizers explaining logistics, risk management, public relations and cybersecurity.

Hiroyuki Ishige, secretary general of the Japan Association for the 2025 World Exposition, said cooperation with participating countries is "the most crucial factor for the expo's success."

Along with pavilion construction, participants are entering the final phase of preparing food procurement and hygiene management.

The organizers plan a soft opening with 90,000 people a week before the event officially opens to the public. During the three-day test run, 40,000 residents of Osaka Prefecture will be invited to participate, allowing them to enter pavilions.

Delays in pavilion construction are still a cause for concern for the organizers who have been struggling to shore up advance ticket sales.

Some participating countries have been unable to provide detailed information to the public about their planned exhibits due to construction delays. Others are withholding details to build excitement.

Manatsu Ichinoki, deputy secretary general of the expo association, said quite a few countries were still rushing to finish their pavilion interiors, but "so far I have not received any reports (from participants) saying they cannot make it in time."

"We will just continue making utmost efforts to be ready on April 13," he said.

To minimize queues, visitors are required to book tickets online for specific dates and times, and to enter lotteries for entry to some of the pavilions and special events.

But advance ticket sales remain slower than expected by organizers, standing at 7.7 million as of early February, far below the target of 14 million.

The organizers have been forced to review the ticket reservation system and are now considering introducing same-day tickets to ensure their sales target is achieved and the expo is profitable.

The site's construction cost has nearly doubled from the initial estimate to 235 billion yen ($1.5 billion), with the central government, the Osaka prefectural and municipal governments, and the private sector each bearing a third.