The only subway line serving the venue of the 2025 World Expo in Osaka was suspended late Wednesday due to a power outage, stranding many visitors inside the venue well into the night and causing the opening to be delayed the following day.

The Osaka Metro Chuo Line, which is the only train service providing direct access from the city center to the expo venue, was halted at around 9:30 p.m. local time on Wednesday, 30 minutes before the expo usually closes, leaving large crowds unable to return home.

About 30,000 people were inside the venue as of 9:30 p.m. local time on Wednesday, according to expo organizers. Shortly before midnight, access to Yumeshima Station, the nearest stop to the expo venue, was restored, but many visitors remained stuck.

While the exact number of those affected is unclear, many visitors and expo staff were believed to have stayed overnight, Kyodo News reported.

Following the subway suspension, many visitors were seen sitting in rows beneath the expo's giant wooden structure, known as the Grand Ring, as midnight approached, the report said.

Local authorities said that a total of 36 people were taken to hospitals by Thursday morning due to suspected heatstroke or other ailments, but none of the cases were serious.

Full service on the Chuo Line resumed at around 5:25 a.m. local time on Thursday. The expo opened 30 minutes later than usual at 9:30 a.m. local time on Thursday following the night of chaos.

"We are sorry that many people had to go through a tough time," a senior official of the Japan Association for the 2025 World Exposition told a press conference on Thursday.

Osaka Metro also apologized during a separate press conference, blaming the outage on an issue with the powered rail alongside the tracks.