State media said the pipeline blew up late on Friday. More than 2,000 firefighters worked overnight to control flames and further blasts on a second pipeline. Officials said nobody was killed.
China Central Television showed the fire raging among tanks at the port in the northern city of Dalian, and eyewitnesses reported flames 100ft high.
The cause of the explosion is still under investigation.
One news agency said it happened when a Liberian tanker was unloading oil at the port but said the tanker had left safely.
A vast stretch of polluted sea is the challenge now facing officials. About 20 boats were last night trying to clean up a dark brown slick of oil and pollution at least 19 square-miles off Dalian's Xingang Harbour.
The pipelines are owned by China National Petroleum Corporation, which is Asia's biggest oil and gas producer.
Phones at the state-owned company's Beijing headquarters rang unanswered, and while the company website showed updates yesterday, there was no mention of the fire. Dalian's secretary general Xu Guochen said firefighters had turned off valves on all oil tanks at the site.
He said the flames gave off gas containing sulphur and aromatic hydrocarbon but insisted these were not such a health risk as to threaten lives. Environmental protection officials said the scene remained unsafe because of toxic chemicals in the air. Dalian's downtown was thick with smog. China National Radio said officials were considering the evacuation of about 600 homes nearby.
Glasgow City Council famously signed a twinning agreement with Dalian in 1987. It is the second largest city in Liaoning Province, Dongbei, north-east China and its largest northern port as well as a tourist resort.