SEOUL, South Korea (AFP) — Six people have been killed after a bus and truck crash caused a huge fire at an expressway tunnel on the outskirts of Seoul, the local fire department told AFP.

Images of the scene in local media showed huge flames and plumes of smoke rising from the tunnel, as hundreds of firefighters battled to bring the blaze under control.

The fire started when a bus collided with a truck at around 1:50 p.m. in the expressway tunnel in Gwacheon, an official at the Gwacheon fire department told AFP.

The raised tunnel, which is designed to protect surrounding buildings from the noise of the road, was quickly engulfed in flames, images in local media showed.

Firefighters have brought the blaze under control, the official said.

"We are doing a search inside the tunnel in case of additional casualties," the official added.

Around 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.