A 7.3-magnitude earthquake shook Japan early Saturday, the U.S. Geological Survey reported.
The quake was off the Fukushima region of Japan, 231 miles east off the island of Honshu.
It was 6.2 miles deep, officials said, hit at 3:10 a.m. Saturday local time and was felt 300 miles away in Tokyo.
The Japan Meteorological Agency reported a one-foot tsunami was observed after it issued a yellow-colored warning Saturday morning, meaning a small tsunami could reach the coast at Fukushima, site of Japan's 2011 nuclear power plant disaster.
There were no immediate reports of damage from the temblor, which Japanese authorities classified as ranging from magnitude 6.8 to 7.1. No irregularities were reported at the Fukushima Dai-ichi nuclear plant. A spokesman at Tokyo Electric Power Co (TEPCO), which operates the plant, told Reuters some workers had been told to evacuate to higher ground.
A yellow warning is issued when a tsunami is not expected to exceed three feet, significantly smaller than the tsunami that hit the energy plant in March 2011.
Yellow tsunami advisories are the lowest of three categories of alert issued by the Japan Meteorological Agency, below red-colored tsunami warnings and purple-colored major tsunami warnings.
No warning for the rest of the Pacific was posted by the U.S. Tsunami Warning Center after the quake.
Japan's nuclear reactors are still suffering from the 9.0-magnitude quake that struck in 2011: Only two of 50 across the country are back online since the quake and its resulting tsunami. The Dai-ichi nuclear power plant was rocked by huge radiation leaks.
About 19,000 people were killed in the 2011 disaster.
NBC's Arata Yamamoto contributed to this report.
