| The nuclear crisis has overshadowed the relief and recovery efforts underway for the quake victims [EPA]
Plutonium has been found in soil samples taken from the Fukushima Daiichi nuclear plant, operator Tokyo Electric Power said as efforts to bring the situation at the earthquake-stricken facility continue.
The samples were taken a week ago but the levels didn't pose a risk to human health, said Sakae Muto, TEPCO's vice-president.
Radiation above 1,000 millisieverts per hour has also been found in surface water in trenches outside the plant's Unit 2 reactor.
Monday's findings came after the company admitted to a radiation reading blunder at the plant, in which officials had reported that levels of radiation at the complex were 10 million times higher than normal.
The inaccurate reading forced emergency workers to flee from the Unit 2 complex on Sunday.
"The number is not credible," Takashi Kurita, spokesman of Tokyo Electric Power (TEPCO), said. "We are very sorry."
But the Japanese government called the mistake "unacceptable".
"Considering the fact that the monitoring of radioactivity is a major condition to ensure safety, this kind of mistake is absolutely unacceptable," Yukio Edano, a top government spokesman, said.
'Sneaking back home'
Al Jazeera's Wayne Hay, reporting from the town of Yamagata, said "the government is very concerned about this miscommunication".
"The residents who lived in the 20km radius of the plant, they want information. We have heard that people have started to sneak back to their homes to get a glimpse of their property."
The company later issued a much lower - but still dangerous - figure, saying radiation levels at the plant are at their highest since the tsunami and earthquake struck on March 11 - at 100,000 times above normal in water found at the Unit 2 reactor.
The nuclear crisis was triggered by the earthquake and the tsunami in which the country's nuclear facilities were damaged.
The nuclear crisis has overshadowed the relief and recovery efforts underway for the quake victims.
The high level of radiation is most likely due to a partial meltdown, in which fuel rods could have overheated after the tsunami knocked out its cooling system, officials said.
"Reactor number two is the one where they had the very high level, coming from pools of water forming in all four reactors," our correspondent added.
"They seem to think that it is coming from reactor two itself. The concern is that water is seeping out and draining into the ocean."
Earlier on Monday, Japan lifted a tsunami warning issued after a 6.5-magnitude earthquake hit its eastern coast.
The Japan Meteorological Agency had announced that a tsunami of up to a half metre could wash into Miyagi Prefecture.
According to the US Geological Survey, the quake struck at 7:23am Japan time (2223 GMT Sunday) near the east coast of Honshu.
The USGS said the quake was 5.9km deep.
Our correspondent reported that Monday's quake was one of the stronger aftershocks since the devastating earthquake of March 11.
"We are about 100km from the coastline where the earthquake hit, and it was strong here as well and was felt even in Tokyo.
"There is no panic here ... and people have been evacuated from towns close to the destruction ... there have been a number of tsunami warnings since and people are getting used to them," he said.
The magnitude 9.0 quake off Japan's northeast coast on March 11 triggered a massive tsunami that decimated cities and towns and killed an estimated 18,000 people.