SEOUL, South Korea — At least 14 people watching a Korean pop band perform at an outdoor concert were killed on Friday when the ventilation grate they were standing on caved in, fire officials said.

Twenty-five people plunged 66 feet to the surface below after the steel grids at the top of the raised ventilation platform collapsed, said a fire official who spoke on the condition of anonymity until there was a formal announcement. An additional 10 people were injured, he said. The local news media reported that some of the injured were seriously hurt and that the death toll could rise.

About 1,000 people had gathered to watch the concert at Pan-gyo Techno Valley, a newly built town that houses many high-tech companies south of Seoul, the capital, local news reports said.

Local television stations showed a gaping hole where the ventilation grate had disappeared. They cited witnesses as saying that a small crowd of people, including office workers from the neighborhood, had climbed onto the grate to get a better view of the performers, including a popular girl band called 4Minute.