A series of powerful aftershocks shook the eastern coast of Japan early Thursday, briefly triggering a tsunami alert, in the wake of a strong earthquake that hit a day earlier.
There were no immediate reports of injuries or damage from the quakes.
The country's meteorological agency said Thursday's temblors were likely aftershocks from a 7.3 magnitude earthquake that hit in the same area Wednesday, shaking buildings hundreds of miles (kilometers) away in Tokyo and triggering a small tsunami.
The series of aftershocks included a magnitude 6.8 quake that struck at 6:24 a.m. local time, and a magnitude 6.1 temblor about three hours earlier, the agency said.
A tsunami alert was issued after the stronger of the two in Fukushima Prefecture in central Japan, but it was lifted a short time later.
All of the earthquakes were centered in an area about 90 miles (150 kilometers) off Japan's northeastern coast, about 270 miles (440 kilometers) northeast of Tokyo. They struck at depths of between 5 and 6 miles (8 and 10 kilometers).
Japan lies on the "Ring of Fire" _ an arc of earthquake and volcanic zones that stretches around the Pacific Rim and where about 90 percent of the world's quakes occur.