A military truck carrying missile parts exploded inside a South Korean highway tunnel on Tuesday, according to YTN television.
The truck was in a four-vehicle convoy when its brakes failed on a highway linking the southern city of Taegu and Masan, just west of Pusan where a summit meeting of the Asia-Pacific Economic Cooperation forum is scheduled to be held later this month.
No casualties were reported.
A police officer said there were reports of a fire but could not provide further details. It was not immediately clear whether the truck was South Korean or belonged to the U.S. military, which has troops stationed in the country.
A South Korean Defense Ministry official said officials were following reports of an accident in the region but could not provide details.
The truck was reportedly carrying missile propulsion devices.
Sparks flew from one of the brakes and caught fire in the cargo compartment of the truck.
Another witness said the trucks were marked with signs indicating explosive materials were on board, Reuters reports.