A key oil pipeline in China's quake-hit southwest resumed operations on Wednesday, a day after they were suspended by PetroChina as authorities drained a dangerous 'quake lake,' state media said.

China National Petroleum Corp (CNPC) officials said operation of the pipeline, some 60 kilometres downstream from the Tangjiashan lake, was halted Tuesday due to safety concerns as drainage work on the body of water sped up.

CNPC said the pipeline resumed operations on Wednesday, after it was deemed safe to do so since the flow of water from the quake lake had slowed, Xinhua news agency reported.

As the only refined oil pipeline to southwestern China, it supplies 70 percent of oil products used in Sichuan and the neighbouring municipality of Chongqing, the company has said.

The pipeline has the capacity to transport more than six million tonnes of oil products a year.

The Tangjiashan lake was created when landslides blocked a river in a particularly remote and mountainous area of Sichuan during the May 12 quake, the worst natural disaster to hit China in a generation.

The quake has left nearly 87,000 people dead or missing.