Rescue workers needed to dig through rubble

The blast at the Gouxi factory in Xinji, Hebei province, completed destroyed the main workshop and buildings nearby, the official Xinhua news agency said.

The cause of the explosion was not immediately known and it was not clear how many workers were in the factory at the time.

Last January, more than 40 people died in an explosion at a fireworks factory in the eastern province of Jiangxi.

The injured in Tuesday's blast were taken to hospital, and 50 people with minor injuries were released, according to Chinese state television.

"I thought it was an earthquake. I was really scared. My sister and I just ran out of the house," Qian Yun, a 19-year-old living about 5 kilometres (3 miles) away from the factory, told the Associated Press.