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A strong earthquake jolted northern Japan early Thursday, injuring at least 99 people and affecting output at some high-tech factories. Hundreds were trapped in trains after the preliminary magnitude 6.8 quake struck shortly after midnight in a sparsely populated region. Police said nearly 100 have reported injuries so far, at least 17 seriously in falls or hit by broken glass. Clean up began almost immediately, but officials warned of possible landslides. Nuclear power plants in the region were not affected, while Fujitsu and NEC closed chip-making plants for checks after the quake. Japan is one of the world's most seismically active countries, accounting for 20% of earthquakes of magnitude 6 or higher. A June trembler in the same area killed at least 10 and left as many missing. Dan Sloan reporting.