A big fire at a Taiwanese-owned molding facility in Shenzhen, Guangdong province may have been caused by overheated injection presses.

According to local media reports and government announcements, shortly after 3pm on Jan 16, a fire was sparked in a four-story building, where more than 400 employees were at work. The blaze quickly spread in the building, owned by Nishoku Mold Industry Co. Ltd., which makes injection molded cell phone housings.

Alarmed by the smoke, thousands of workers at nearby factories were evacuated. The blaze was brought under control within four hours by at least ten fire trucks.

Shenzhen officials said initial investigation pointed to overheated injection machines igniting inflammatory chemicals as a likely cause of the fire. However, there were also accounts by witnesses quoted in media reports, claiming short-circuited ultrasonic equipment sparked the flame.

By Jan 18, six of the 21 injured workers remained hospitalized.