A huge explosion at the chemical factory Mitsubishi Materials in Yokkaichi city, central Japan, has killed at least five people.

Other 12 people have been reportedly injured.

The blast occurred in the afternoon at the chemical plant in Mie prefecture.

Maintenance crews were cleaning out a heat exchanger used in the production of silicon products when the blast happened, officials said.

It is not clear at this stage what caused the explosion.

The plant manufactures polymers and uses a number of highly-volatile chemicals including hydrogen and chlorine.

Mitsubishi Materials plant manufactures polymers and uses a number of highly-volatile chemicals including hydrogen and chlorine

Thursday’s blast at the plant – based some 220 miles west of Tokyo – killed five of the maintenance workers on the spot.

The number of injured has ranged, in reports, from 12 to 17.

Emergency officials said there had been no fire and the situation was quickly contained.

Mitsubishi Materials – a division of the huge Mitsubishi Corporation – makes a range of automotive, electronics, and construction and engineering products.