The world's biggest shipping companies continue to call at Japanese ports having decided that there is no real threat of radiation coming from the wrecked nuclear power plant, reports Bloomberg.

Having initially pulled out, Hapag-Lloyd, the world's fourth biggest container shipping line, has resumed calls at Tokyo and Yokohama, meaning that none of the world's 16 biggest container carriers are avoiding the area as some did at first.

Ships still shun a 20-mile exclusion zone around the Fukushima Dai-Ichi plant, but that is some 200 miles from Tokyo.

Despite record readings of contaminated water, the UN's International Maritime Organisation IMO said there was no medical basis for restricting shipping and the US Navy said any radiation on ships could be cleaned with soap and water and it isn't harmful to health.

"The bottom line is that people haven't been avoiding Tokyo, they're just being more careful about how they approach it," Citigroup Global Markets analyst Christian Wetherbee told Bloomberg from New York.

Cosco, NYK, MOL, "K" Line and China Shipping said there are no changes to their usual services. Their fleets can carry about 85 million tonnes of cargo including coal, iron ore and grains, according to data from Clarkson Research Services, a unit of the world's largest shipbroker.