A powerful blast has struck a chemical factory in central Japan, killing at least five and leaving 17 injured, reports local press. Japanese police say the explosion was triggered by a chemical reaction inside the plant.

The incident happened at a chemical plant owned by Mitsubishi in Yokkaichi, Mie Prefecture. The factory produces silicon materials for the international firm.

"There was some explosion triggered by some sort of chemical reaction during plant operations," said a police spokesman in Mie, central Japan to AFP.

Japanese Broadcaster NHK reported that at least five people had died in the blast at the Mitsubishi Materials Corp chemicals plant. The local fire department said they could not confirm any casualties, but did tell Reuters that 17 people had been injured, five of them seriously.

Maintenance of a heat exchanger used in the production of silicon products was reportedly being carried out when the blast occurred.

"Some 170 people were working at the plant," a Tokyo-based spokesman said. "Operation at the plant has been suspended. We still don't know the cause of the explosion."

Twin explosions struck a chemical plant in south-west Japan in April 2012, killing one person and injuring another two. The blasts happened at Mitsui Chemicals in Yamaguchi prefecture after workers tried to shut down part of the plant following a problem in a different sector. The massive blast, which was caught on video, damaged hundreds of homes nearby.