Citizens' groups have called for pregnant women and children to evacuate Fukushima City.
Soil radiation in a city 40 miles from Japan's stricken nuclear plant is above levels that prompted resettlement after the Chernobyl disaster.
The highest level was 46,540 becquerels per kilogram exceeding Japan's legal limit of 10,000 becquerels per kilogram.
Soil radiation in a city 60 kilometers (40 miles) from Japan's stricken nuclear plant is above levels that prompted resettlement after the Chernobyl disaster, citizens' groups said Tuesday.
The survey of four locations in Fukushima city, outside the nuclear evacuation zone, showed that all soil samples contained caesium exceeding Japan's legal limit of 10,000 becquerels per kilogram (4,500 per pound), they said.
The highest level was 46,540 becquerels per kilogram, and the three other readings were between 16,290 and 19,220 becquerels per kilogram, they said.
The highest reading in the city of 290,000 people far exceeded the level that triggered compulsory resettlement ordered by Soviet authorities following the 1986 Chernobyl nuclear disaster in Ukraine, they said.
The citizens' groups -- the Fukushima Network for Saving Children from Radiation and five other non-governmental organizations -- have called for the evacuation of pregnant women and children from the town.
Kobe University radiation expert professor Tomoya Yamauchi conducted the survey on June 26 following a request from the groups.
"Soil contamination is spreading in the city," Yamauchi said in a statement. "Children are playing with the soil, meaning they are playing with high levels of radioactive substances. Evacuation must be conducted as soon as possible."
The coastal Fukushima Daiichi plant has been spewing radiation since the March 11 earthquake and tsunami knocked out its cooling systems.