Tokyo: A powerful aftershock has rocked an area of Japan still reeling from the deadly March 11 earthquake and tsunami disaster, the US Geological Survey said on Friday.
The 6.1-magnitude quake struck at 12:58 (14:58 GMT Thursday), 276km east of Sendai, Honshu Island, at a depth of 24km, the USGS said.
There were no reports of any damage or casualties and no threat of a tsunami.
The biggest ever quake recorded in Japan struck on March 11, triggering a huge tsunami and leaving 13 591 people dead, with another 14 497 still unaccounted for.
Tens of thousands of people lost their homes, while many others were forced to evacuate after a series of explosions at the Fukushima Daiichi nuclear plant sent radiation spewing into the air.
The radiation leaks have resulted in bans on produce from the affected area and hurt the fishing and farming industries because of public fears over radioactivity in food.
Workers at Fukushima entered a reactor building on Thursday for the first time since an explosion sparked the nuclear crisis.
Wearing gas masks and protective suits with oxygen tanks on their backs, two workers stepped into the building housing reactor number one - one of four reactors badly damaged at the plant - to gauge radiation levels.
The company later sent in more workers to set up a ventilation system to filter radioactive material out of the air within the reactor building, the officials said.