Four aftershocks measuring 5.0 or more on the Richter scale shook Japan's northern Hokkaido island today, two days after nearly 600 people were injured by a powerful earthquake which rattled the region.
Officials said aftershocks were partly to blame for a fire which broke out at an oil storage tank in Tomakomai, a coastal city on the island.
Experts warned residents to not to let down their guard. "Aftershocks could cause damage," an official at Japan's Meteorological Agency said, but he admitted the immediate chance of another major earthquake was diminishing.
"The possibility of strong aftershocks hitting the region is expected to decline as time goes by," the official said.
But Friday's earthquake - which at 8.0 on the Richter scale was more powerful than several previous, more deadly ones elsewhere in quake-prone Japan - could still trigger tremors and landslides, he added.
A total of 37 aftershocks have been felt in the relatively sparsely populated region since Friday's quake. Police said at least 589 people had been injured.
The initial quake destroyed or damaged more than 100 buildings and forced around 13,000 people to evacuate their homes.