Britain's Sellafield nuclear fuel reprocessing plant said it had detected higher than usual levels of radiation and ordered all non-essential staff to stay at home.

Sellafield, the site of Britain's worst nuclear accident in 1957 and once the producer of plutonium for nuclear bombs, said there was no risk to the public, a statement echoed by the government.

The operator said the facility, just outside Britain's striking Lake District national park on the coast of the Irish sea in northwest England, was operating normally.

A higher than normal radiation reading was logged overnight via an air monitor at a perimeter fence, but Britain's state nuclear decommissioning agency, which owns the site, said the source of the reading was unclear.

"It is far too early to say there is a leak. Everything being done is precautionary. There is no danger to the workforce, communities or wildlife," said Bill Hamilton, a spokesman from Nuclear Decommissioning Authority.

"At the moment we don't know where the radiation is coming from."

Sellafield, a patchwork of grey buildings, industrial cylinders and cooling towers surrounded by grassland, said the decision to keep staff at home was conservative.

"As a result of a conservative and prudent decision, the Sellafield site is operating normally but with reduced manning levels today," Sellafield said in a statement, adding that only essential workers were being asked to report to work.

The British government said it was in constant contact with the site, about 480km northwest of London, and that there was no risk to the public from the raised level of radioactivity.

Once the source of plutonium for Britain's nuclear bombs, Sellafield was the site of the October 1957 Windscale fire, Britain's worst nuclear accident, when a plutonium reactor burned for five days, belching radiation into the atmosphere.

It is the site of a civilian nuclear power station that is being decommissioned by a consortium of British company Amec, French group Areva, and US firm URS.

Now one of two nuclear fuel reprocessing plants in Europe along with Areva's La Hague plant in France, Sellafield receives spent fuel from power plants across the world, including Japan. It employs over 10,000 people.

Alongside government and company assurances that there was no danger to the public, nuclear experts and academics said initial information available to the public indicated this was a minor incident.-Reuters