Heavy fog caused the pile-up of 28 vehicles on an expressway in east China's Anhui Province on Monday, killing at least nine people and injuring 30 others, the local expressway administration said.

Eighteen successive collisions took place between 4 a.m. and 6 a.m. within a three-kilometer section of the freeway linking the provincial capital of Hefei to Nanjing, capital of neighboring Jiangsu Province.

The tragedy was caused by fog that began to envelop the road at 2 a.m. Monday. The traffic administrators had warned drivers about the fog, which gradually turned thick and triggered the first accident two hours later.

The injured people have been hospitalized and rescue workers are clearing the site.