TOKYO : An explosion at a Japanese factory that had previously attracted the attention of safety inspectors killed at least five people and injured a dozen more Thursday.The blast happened in the early afternoon at the plant in the central city of Yokkaichi, when maintenance crews were working on a heat exchanger used in the production of silicon products, a plant spokesman told AFP.Initial reports put the death toll at two, but they were quickly revised upwards.“Five people are dead. 12 people have been injured, of whom nine sustained only minor injuries,” said a spokeswoman at Mie prefectural police.A separate police spokesman told AFP the plant, run by Mitsubishi Materials, makes parts for solar panels and automobiles, using polymers made from silicon, hydrogen and chlorine. “An explosion occurred but there is no fire. We received an emergency call at 2:09 pm (0509 GMT)...and at 2:21 pm the incident appeared to have calmed down,” he said.Television footage showed around a dozen firefighters setting out stretchers for victims at the site, where a pipe appeared to have fallen to the ground and other machinery parts were scattered nearby.“I heard a boom and saw white smoke rising from the plant,” a 56-year-old worker at a nearby plant was quoted by the Sankei Shimbun as saying. “I don’t remember there ever being such a serious accident in Yokkaichi before.”A separate police spokeswoman said detailed inspections to determine the cause of the accident had not yet begun because of the danger of secondary explosions, although she added that there was no known risk of a toxic chemical leak.Hiroki Morofuji, an official at the plant, said the blast had involved maintenance workers at the premises, which are sited in a heavily industrialised region.Mitsubishi Materials, headquartered in the Japanese capital, makes a range of products including auto parts, silicon wafers for memory chips used in consumer electronics, and cement for road and bridge construction.“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.”He confirmed a report by Dow Jones Newswires that the Yokkaichi factory was ordered by local officials to shut down for several months in 2010 after an on-site inspection discovered it was generating high-pressure gas without necessary permits.The company, which reported sales of about $12.2 billion in its latest fiscal year, has more than 22,000 employees and operations across the globe including in the United States, Brazil, Germany and India, according to its website.The death toll is the largest in an industrial accident in Japan since an undersea tunnel collapsed at an oil refinery in February 2012, trapping five people.In October last year a fire at a hospital in southern Japan killed at least 10 elderly people, including staff.