Chaos and confusion marred the Culture Center at Expo 2010 Shanghai on Sunday, as tens of thousands scrambled to get into a concert by South Korean pop music singers.

Crowds started to form in the wee hours at the Expo gates on Sunday, and soon mobbed the Culture Center, where free concert tickets were handed out.

Scuffles and arguments broke out among fans - mainly teenage Chinese girls - and security staff, with many suffering scratches and sprains.

At around 10 pm on Sunday, hundreds of young fans were still crowding around the cordoned-off Culture Center in the shape of a gigantic seashell, shouting, "Let us in!" and questioning the managerial ability of Expo organizers.

"I have never seen such chaos at previous concerts," said Guo Zhu, a Shanghai student who failed to see the performance by artists including Super Junior, KANGTA and BoA on Sunday.

"We read from the newspaper that 5,000 free tickets would be given away, but they were quickly gone and security staff told us only a few hundred were distributed," she said. "They are cheating us."

Another girl, surnamed Xie, told China Daily that many people were pushed down by surging crowds and suffered injuries, and that security staff was increased only when the organizers realized the huge popularity of the concert.

"But that was too late," said Xie, who arrived in early morning and hadn't had a meal all day. "Girls beside me tumbled row after row during the pushing and shoving. Shoes and other belongings are everywhere after the crowds were evacuated."

Fans also said that no one gave them proper information about the concert, and the distribution of the tickets turned into a melee. Instead, scalpers were seen at the Expo site, where the "free tickets" were being sold for 300 to 3,000 yuan.

The Expo spokesperson's phone went unanswered on Sunday night. Officials at the South Korean Pavilion said they were also shocked by the chaos.

"We had strengthened our security force in the morning, but the situation was still hard to control mainly because many were overreacting when they didn't get their ticket," said Kim Minhwa, press officer of the pavilion.

But she denied that most tickets were retained by the organizers, and was not aware of any casualties from the chaos.

The official also said another performance by South Korean singers will be held in the Expo Garden in August. Considering the situation on Sunday, the next one will be more carefully arranged, she said.