At least 16 people were killed and 11 others injured on Friday after a ventilation grill they were standing on while watching an outdoor concert fell 20 meters down a shaft, South Korean officials said.

Close to 700 people had gathered in the streets of southern Seongnam, Seoul on Friday to watch a concert that featured performances from popular artists including Kpop girl group 4Minute. The concert had been part of a festival hosted at the Pangyo Techno Valley.

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Because of the jam-packed venue, several concert-goers decided to climb on top of a ventilation grate to gain a better view. But the grate soon collapsed under the heavy weight, BBC relayed.

The ventilation grate, estimated to measure 3 to 4 meters wide, covers an elevated shaft 20 meters deep over an underground parking lot.

I heard loud screaming and when I looked over, it seemed as if the people were being sucked down into a vacuum, a witness on the scene shared.

Fire officials who spoke on condition of anonymity said 12 people had died on impact while two others passed away en route to the hospital. The others are presumed to have died while receiving treatment at the hospital, according to South Korean news agency Yonhap.

Eleven people are in critical condition, a local official revealed at a televised conference.

No additional details on the victims have yet been released but several witness accounts claim most of the audience were female students.

Rescue efforts are still underway but local officials warn that casualty figures may still rise.

Seoul-based BBC correspondent Steve Evans speculates the accident may bring forward the issue of South Korean safety standards.

Following the Sewol ferry disaster in April, many have called for an overhaul of Seoul's safety regulations which has fallen behind the culture of prioritizing economic development above all else.

Tags4Minute concert, South Korean safety regulations, South Korean concert, concert accident