Firefighters walk out of Seoul Subway Line 9's Heukseok Station on July 1, 2024 in Seoul, South Korea, after smoke from an unknown source was seen at the station at around 4:42 pm on this day. The train was asked to pass through the station without stopping. Officials say investigations are ongoing. Meanwhile, Dogok-Daechi Station on Line 3 was suspended due to smoke around dawn that day. Photo: VCG