A huge blaze has broken out at steel plant near Tokyo's Haneda airport, with television images showing plumes of thick black smoke and flames shooting into the air.
The fire comes just hours after a blast ripped through a warehouse at a US military post near Tokyo, sending sparks into the sky and triggering a blaze that burned through the night.
Local police declined to speculate on whether there was any link between the two incidents.
"We do not know any details at this point," a police spokesman said.
The site near the busy international airport is owned by a unit of giant steelmaker Nippon Steel & Sumitomo Metal.
The vast steel pipe-making facility, which spans 20,800 square metres, operates a pair of manufacturing lines about one kilometre from Haneda.
"A fire broke out from a two-metre cooling tower," a fire official said.
Aerial television footage showed the blaze stretched across a long, narrow warehouse after it was first reported just before midday local time.
It has reportedly spread to a next door cosmetics factory owned by Japan's Kao.
Public broadcaster NHK said about 600 of its employees had been evacuated from the site.
There was no word about employees working at the Nippon Steel factory, or if anyone at either site was injured.
Japan Airlines and rival All Nippon Airways said none of their flights had so far been affected.
Last year, at least 15 people were injured after an explosion at a Nippon Steel plant in central Japan.
It followed a series of accidents at the site, which prompted the mayor of Tokai, a city of about 100,000 people, to formally ask the steelmaker to draw up a plan to deal with any safety problems.