The blaze broke out after a freight truck collided with a bus on a highway near Seoul, injuring 37.
At least five people have been killed and 37 injured in a fire caused by a freight truck colliding with a bus in a highway tunnel near the South Korean capital, Seoul, officials said.
It was not immediately known what caused the collision and the fire on Thursday and what cargo the truck was carrying.
The blaze erupted when the vehicles collided at about 1:50pm (04:50 GMT) in an expressway tunnel in Gwacheon, a fire department official told the AFP news agency.
Fire officials said the collision occurred inside a noise-barrier tunnel on the highway. The raised tunnel is designed to protect surrounding buildings from the noise of the road.
Three of the injured were in serious condition, while 34 suffered light injuries, according to the National Fire Agency.
Enormous plumes of fire and thick smoke were seen coming from the tunnel in images posted on local and social media.
Hundreds of firefighters managed to bring the blaze under control.
“We are doing a search inside the tunnel in case of additional casualties,” a fire official said.
About 20 people are being treated for smoke inhalation, he added.
Interior minister Lee Sang-min called for “maximum resources deployed” to save lives, the Yonhap news agency reported.
“I urge the authorities to put out the best efforts to save the lives of those who have not escaped,” he said.
In October, at least 153 people were killed in a Halloween crowd crush in Seoul’s Itaewon nightlife district.
A series of preventable disasters – including Itaewon and the Sewol ferry sinking which killed more than 300 people in 2014 – has shaken public confidence. Many South Koreans have questioned whether safety standards were sidelined and regulations ignored in the government’s rush for development.