The fire has been put out and barricades have been set up to stop the oil from entering the sea. (Reuters)

At least 22 people were killed when a leaking petroleum pipeline caught fire and exploded on Friday in China's coastal city of Qingdao.

The number of injured people have not yet been confirmed. They are being treated at local hospitals, state-run Xinhua news agency reported.

The accident happened around 10:30 am in Huangdao district when workers were repairing a leaking petroleum pipeline, the Qingdao government's publicity office said.

Oil supply through the pipeline was stopped in the early hours.

The fire has been put out, and barricades have been set up to stop the oil from entering the sea, the Qingdao municipal environmental protection bureau said.

The 176-km pipeline, which links oil depots in Huangdao to Weifang city, home to a few petrochemical plants, is owned by state-run 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, the Xinhua report said.

Officials in the city's maritime safety administration said 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.

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.

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