A fire broke out on Tuesday at a Nippon Steel plant in southwest Japan, forcing the world's second-biggest steelmaker to halt some blast furnace operations from 11:00 a.m. local time.
A company spokesman said there were no reports of injuries at the Yawata Works. The plant employs 2,950 and had crude steel output of about 4 million tons in 2007, accounting for 12 percent of the group's total output.
Nippon Steel said it had not decided whether to halt all production lines at the 15 million square metre Yawata works, which makes a range of products such as bar steel, steel pipes and steel sheets.
Shares in Nippon Steel were down 2.8 percent in morning trade to 594 yen compared with a 2.2 percent fall in the benchmark Nikkei average.
A spokesman said the fire, which was discovered at 6:37 a.m., began on a coke-carrying conveyer belt apparatus that then collapsed, damaging pipes carrying inflammable gas outside the building, he said.
He said the plant itself was not on fire but firefighters were dousing it with water to prevent the blaze from spreading.
TV footage showed flames shooting out from smokestacks and other parts of the plant, and an aerial shot showed the entire plant shrouded in thick black smoke.
A local police spokesman said firefighters were no longer trying to put out the fire, but were instead letting the flames die out to prevent the spread of gases.
"We expect it will take about 20 hours for the flames to go out," he said by telephone.
Carbon monoxide levels were safe for now, but officials were checking for other gases, he added.