FUSHUN, Liaoning -- An explosion at a northeast China oil refinery Wednesday injured at least 30 workers, officials have confirmed.

The blast at about 9 a.m. ignited a blaze at the refinery in Fushun city, Liaoning province, said a spokesman for the Publicity Department of the Fushun Municipal Committee of the Communist Party of China.

The workers were injured by broken glass and other debris, said an official surnamed Wang at the Information Center of the Fushun Petrochemical Company.

All of the injured had been taken to hospital and most were only slightly injured.

No fatalities have been reported so far.

Firefighters have brought under control the fire at the No 2 plant of Fushun Petrochemical Company, a subsidiary of China National Petroleum Corporation.

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The explosion occurred at the heavy oil catalytic cracking unit, part of an automated production line.

Thick smoke was hovering over the refinery, blotting out most of the sky, witnesses said.

"I ran out and saw flames several meters high at the refinery plant," said a witness. "As few people were in the plant and the control room had blast-proof facilities, there might be few severe casualties."

The municipal government initiated an emergency response to the incident. The cause of the explosion is under investigation.

Fushun Petrochemical Company, with total assets of 20.9 billion yuan ($3.2 billion), has a crude oil processing capacity of 10 million tons annually.

A blast happened at Fushun Petrochemical Company's No 3 oil plant, on Sept 7 last year, but no casualties were reported and the fire was put out in an hour.