Crisis-stricken Japan, which has yet to gain a definite hold on how to arrest the radiation problems of a nuclear plant downed by an earthquake two years ago, has again been shaken by a strong 6.9 magnitude quake on Wednesday.

The quake shook Japan's eastern provinces as well as Tokyo. Its center was recorded offshore near Torishima, part of the Izu Islands about 600 kilometres (370 miles) south of Tokyo.

p-wave and s-wave from seismograph

Although far from the mainland, residents reported experiencing tremors at the north of the main island of Honshu to the west. Buildings also reportedly swayed for a few moments in Tokyo.

As a precaution, some train lines suspended operations for a while to conduct safety checks. They immediately resumed.

Although strong, no tsunami alert was issued relative to the Wednesday shaker.

Officials at Tokyo Electric Power (Tepco), operator of the currently crisis-stricken Fukushima Daiichi nuclear power plant, said the quake did not do any damage to the already radiation-leaking plant.

"We have confirmed that there was no immediate abnormality," an unidentified Tepco spokesman was quoted by the AFP, citing data collected by monitoring equipment. The official said they will continue to patrol the plant to personally check for any physical damage the latest quake might have caused.

The Nuclear Regulation Authority confirmed the absence of abnormalities at the Fukushima Daiichi nuclear power plant, as well as with the two other nuclear plants in northern Japan.

On Tuesday, Prime Minister Shinzo Abe's government said it will release $500 million to help control the continuous leaks from the plant, as well as decontaminate its highly toxic water.

"The world is watching to see if we can carry out the decommissioning of the Fukushima nuclear power plant, including addressing the contaminated water issues," Mr Abe reportedly told cabinet ministers.