At least 35 people were killed after a leaking pipeline caught fire and exploded on Friday morning in the coastal city of Qingdao, in east China's Shandong Province, local authorities said.

The number of injured people have not yet been confirmed. They are being treated in local hospitals.

The cause of the accident is being investigated. But authorities have ruled out that it was linked to a terrorist attack.

The accident happened around 10:30 a.m. in Huangdao District when workers were repairing the petroleum pipeline, which began leaking oil at around 3 a.m., according to the Qingdao government's publicity office.

Oil flow through the pipeline was shut down at about 3:15 a.m.. The fire has been put out, and barricades have been set up to stop the oil from entering the sea, according to a comment posted on Friday afternoon on the official microblog of the Qingdao municipal environmental protection bureau on Sina Weibo, China's Twitter-like microblogging service.

The 176-km pipeline, which links oil depots in Huangdao to Weifang City, home to a few petrochemical plants, is owned by Sinopec, China's largest oil refiner.

Pieces of cement and debris were scattered around the explosion site, which is close to the coast.

An oil belt with a length of two to three meters could be seen in waters around the explosion spot as of 2:40 p.m. No new oil leakage from the pipeline had been found, according to a Xinhua reporter at the scene.

While sources with the city's maritime safety administration told Xinhua that they had not received any report on blast-related pollution in the sea so far, they have strengthened patrolling around the coastal areas close to the blast site.

Rescue work continues. The cause of the accident is being investigated.

Photographs posted on Sina Weibo showed the blast caused a large trench in the ground and that car windows nearby were cracked.

Environmental monitoring showed that the concentration of toxic materials in the air is under the national standard. The local government has told citizens to stay calm.

Huangdao District is connected with the city proper by the Qingdao Jiaozhou Bay Bridge.

Xinhua reporters said the exit on the bridge leading to Huangdao has been temporarily closed and only emergency vehicles are allowed to enter. Local traffic authorities have told drivers to allow rescue vehicles to pass.