Workers have removed radioactive soil from a Tokyo playground where extremely high radiation levels had worried local residents for days, official said.

Soil underneath a slide at the park in the northwest of the Japanese capital showed radiation readings of up to 480 microsieverts per hour.

Anyone directly exposed to this level would absorb in two hours the maximum dose of radiation Japan recommends in a year.

Contractors dug out soil from the spot on Friday, and the radiation reading went back to normal, around 0.06 microsieverts per hour, according to local reports.

Workers suspect the contamination was from radium, which is used for medical tools and a glow-in-the-dark paint for watches, reports said.

Yukio Takano, the mayor of Tokyo's Toshima ward where the park was located, said in a statement that the problem that fanned fears for the health of area children was likely to end soon.

"The amount of radiation has been dramatically reduced after a test excavation" of the soil, said the statement, released late Friday.

The contamination came to light after a local resident reported it on Monday but officials say they do not think it is connected to the disaster at Fukushima.

The park was built in 2013, two years after the Fukushima nuclear crisis, a local official told AFP, on what was previously a parking lot for Tokyo's sanitation department.

Top soil at the lot was replaced before the land was turned into a park.

Many families in eastern Japan continue to survey the levels of radioactive contamination around their houses, distrustful of government assurances that most places were not affected by the Fukushima meltdown.

Such efforts have led some people to discover radioactive materials that have been dumped in their neighbourhoods.

Months after the Fukushima crisis started in 2011, officials found bottles of radium discarded under a private house and a supermarket in Tokyo.