Firefighters battled the flames for more than 40 hours before extinguishing them early Tuesday. Authorities were investigating the cause, local fire department spokesman Tatsuhiko Kamara said.
The fire broke out Sunday morning, two days after a magnitude-8 earthquake jolted Japan's northernmost island of Hokkaido. The temblor, which injured almost 600 people, and subsequent aftershocks are believed to have dislodged the storage tank's cover, though it was unclear what ignited its contents.
The tank was filled with 164,000 barrels of naphtha _ a highly flammable petroleum byproduct.
The refinery was safely separated from residential areas in Tomakomai, a city of 173,000 residents, and no injuries were reported. But town officials received hundreds of complaints about the smoke.
The tank was the second at the refinery to catch fire after Friday's earthquake. A tank containing 189,000 barrels of crude oil went up in flames the day of the quake.
There have been five fires over the last three years at the refinery, operated by Idemitsu Kosan Co., a major oil company, including the two quake-related blazes. None have caused injuries.
