Two people were killed and 37 others injured when a freight truck collided with a bus causing a huge fire on a highway near Seoul.

Video footage showed a soundproof awning ablaze soon after it broke out on the Second Gyeongin Expressway near the South Korean capital shortly before 2pm local time.

It also shows lines of burned-out cars still smouldering as firefighters extinguished the flames, with an official saying more than 40 vehicles were destroyed.

One witness told television broadcaster YTN that the heavy traffic made it difficult for vehicles to escape the affected area as the fire quickly spread.

Thick black smoke billows from a noise barrier tunnel along an expressway in Gwacheon, South Korea (Picture: EPA)

The expressway smoulders after the flames were put out (Picture: Reuters)

More than 40 vehicles were destroyed in the blaze (Picture: EPA)

The cause of the fire is being investigated (Picture: EPA)

It wasn’t immediately clear what caused the collision and the fire, or what cargo the truck was carrying.

The National Fire Agency said in a statement that the three of the injured were in serious conditions while 34 others suffered relatively minor injuries.

Earlier TV footage showed thick black plumes of smoke billowing from the tunnel, but fire officials said later they’ve almost put out the blaze.

The public affairs office at the fire agency couldn’t immediately confirm where the five dead came from.

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More than 40 vehicles were destroyed in the blaze near Seoul, with witnesses saying heavy traffic made it difficult for them to escape.