At least 16 people have been killed and 11 injured in an accident at a pop concert in Seongnam, south of Seoul in South Korea, officials say.
They say a ventilation grate collapsed and a group of concert-goers fell 10 metres (33ft) into an underground parking area.
The crowds had been watching an outdoor performance by the popular Korean girl band 4Minute and other bands.
The victims climbed on top of the grate to get a better view of the show.
Rescue workers warn that the death toll may rise.
'Sucked into a hole'
"Twelve people were killed at the scene, two others died while they were being rushed to the hospital. Others are assumed to have passed away while receiving medical treatment," a local fire official was quoted as saying by South Korea's Yonhap news agency.
About 700 people were at the concert, part of a local festival being held at Pangyo Techno Valley, a multi-purpose complex for technology firms.
In the dense crowd, 20-30 people climbed on a grate over the deep ventilation shaft. Under their weight the grate gave way and the group fell through.
"I'm a bit shaken up but I'm OK. I was literally 20 ft away from where it happened. None of us knew what had happened. I was queuing up at the beer tent at the time. The concert had just started," Ross Gibson, who lives in Seoul, told the BBC.
Another eyewitness told YTN news channel: "There was a sudden, loud screaming, and when I turned it looked as if people were being sucked down into a hole."
The BBC's Steve Evans in Seoul says the immediate task was to save the lives of the injured but that the accident may intensify a debate in South Korea about safety standards.
After the Sewol ferry sank six months ago, with the loss of more than 300 lives, many alleged that the country's regulations had not kept pace with its rapid economic development.