Elevated levels of radiation found in a residential area of Tokyo are almost certainly not connected to the stricken Fukushima nuclear plant, officials say.
Japan's science minister said the radiation had been traced to material stored in the basement of a house.
"With the resident's permission we entered the house and measured various parts, and found one spot with high radiation levels," said Setagaya Ward Mayor Nobuto Hosaka on his official blog.
"We then confirmed that high radiation was coming from what seemed to be bottles inside a cardboard box underneath the floor."
Japan's science ministry said officials believed the radioactive material was radium, which is sometimes used for medical purposes, and unlikely to be related to Fukushima, The Wall Street Journal reported.
Yesterday the area along a sidewalk in Tokyo's Setagaya Ward, frequently used by elementary school children, was found to have airborne radiation measuring 3.35 microsieverts per hour.
By way of comparison, the latest readings taken from inside the evacuation zone in Fukushima prefecture, central to the world' s worst nuclear accident in 25 years, measured 2.17 microsieverts per hour, according to local prefectural officials.
The hotspot has been cordoned off and authorities have attempted to reduce the concentration of radiation by using water and "other" methods, local media said, but the levels have remained worryingly high despite the counter-measures, sparking widespread panic around Japan's primary metropolis.
"Honestly, it's shocking that such a high level radiation could be detected in densely populated neighbourhood in the center of Tokyo," said a resident.
An investigation is currently underway to determine whether the troubled nuclear plant in Fukushima is responsible for the high doses of radiation detected in and around Japan's capital city.
Chief Cabinet Secretary Osamu Fujimura said that nuclear agencies and government authorities will increase monitoring activities around the country.
"There will be places with radiation that cannot be detected now no matter how carefully they examine the regions. I am afraid that more places with high radiation levels will pop up in the future," said an old lady.