A furnace exploded Tuesday morning at an iron factory in Asahikawa, Hokkaido, leaving six people injured and prompting nearby residents and workers to evacuate the area for fear of further blasts, police and firefighters said.

Sixteen people were taken to hospital, including one man suffering serious burns after the 8:30 a.m. blast at Hiyama Iron Works Co., but the police confirmed that only six of them sustained injuries. The factory was in operation at the time of the explosion.

The blast shattered windows at the iron factory and left a hole in one of its walls, the police said.

According to the police, six or seven workers were near the furnace used to melt metal. The police suspect melted steel inadvertently touched coolant water, triggering a vapor explosion.

The factory is located about 2 kilometers from JR Asahikawa Station. Hokkaido Railway Co. said it has suspended some train operations.

A 60-year-old man told Kyodo News he heard two loud noises and felt the building shake. "When I looked outside, black smoke was coming from the iron factory," he said.

Hiyama Iron Works, launched in 1923, manufactures iron frames for construction, molds and industrial machinery.