The death toll from Monday's fireworks factory explosion in Northeast China's Heilongjiang province has climbed to 20, with 153 injured and four missing, local authorities said on Tuesday.

The explosion occurred at 9:45 on Monday morning at a factory owned by the Huali Industry Corporation in Wumahe district of Yichun city.

Preliminary investigations showed the factory continued production after operations had been suspended by the local government in June, Sun Yongbo, vice-governor of Heilongjiang, said on Tuesday.

The factory also operated illegally by manufacturing large fireworks when it only had official permission to produce small firecrackers, Sun said.

Huang Yi, a spokesman for the State Administration of Work Safety, said on Tuesday that many fireworks factories neglect work safety regulations in their quest for profit.

Lessons should be learned from the accident in Yichun, he said. The safety loopholes that exist in the industry need to be exposed to the public to avoid similar incidents in the future.

The explosion killed 10 and injured 35 of the factory's 51 workers, while four went missing.

Another eight were killed and 35 injured when the explosion hit the neighboring Taihua Timber Factory, which is also owned by Huali.

The accident also claimed the lives of two pedestrians, and injured scores more in collateral damage.

The fire was largely brought under control on Monday after a helicopter dumped water on the blaze.

But the situation remains serious and there are concerns that further fires could ignite three other timber mills nearby, Xinhua News Agency reported a local government official as having said on Tuesday.