Shanghai - Japanese pop group SMAP's concert at the Expo Cultural Center, scheduled for June 13, has been cancelled due to safety concerns, officials said.

The Expo Coordination Bureau announced the decision on their website and explained the move was to ensure traffic flow and a comfortable visiting experience for the increasing number of visitors to the Expo Garden.

On Saturday, 524,900 people visited Expo 2010 Shanghai, the largest number of visitors on a single day since the event opened on May 1.

However, many believe the cancellation was made to avoid a repeat of the incident on May 30, when thousands of fans for a concert featuring popular South Korean artists were unable to get tickets.

Tickets for the concert were distributed on a first-come-first-serve basis on the day of the event, and turned the ticket release site in front of the Expo Cultural Center into something resembling a battlefield.

The incident left several in need of medical treatment. But Xu Wei, spokesman of the Expo Coordination Bureau, said some disorder during an event of that scale was normal.

The cancelled SMAP show was a big disappointment for fans that had been looking forward to seeing the group's performance. Netizens, again, were the first to express their discontent.

"SMAP's concert was the main reason for my visit to the Expo. I had a ticket and hotel booked.

"Why should I go now?" said one netizen on an online forum of Baidu.

"I was shocked by the reports of the Korean pop concert on May 30," said a netizen named IceCreamCat. "But if organizers don't want this to happen again, why don't they just sell the tickets rather than give them away free?"

SMAP's concert was scheduled for Sunday at the 18,000-seat Expo Cultural Center as part of the celebration of Japan Week following the country's National Pavilion Day on Saturday.

It would have been the group's first performance in China.

SMAP announced their regret that the concert had been cancelled on its official website, but the group said it was hopeful they would perform in China in the future.

Organizers said all performances at the Expo will receive a security evaluation in the future. Those that do not pass the evaluation will be cancelled.