By Chikako Mogi and Randy Fabi
SINGAPORE/TOKYO (Reuters) - Japan's transport ministry on Friday sought to ease growing fears among international shipping lines about the safety of operating in Tokyo and Yokohama, saying radiation at the country's largest ports were at "very safe" levels.
At least two German shipping companies are avoiding Tokyo Bay area ports due to radiation concerns from Japan's quake-crippled Fukushima nuclear plant, sparking worries of new supply chain bottlenecks if others in the industry follow their example.
Radiation levels as of late Thursday in Tokyo's port, located 240 km (150 miles) south of the plant, were below exposure levels the World Health Organization (WHO) considered normal, the ministry said.
"We are offering accurate and timely information. We ask that services to Tokyo and Yokohama ports continue, based on rational and scientific judgment," a ministry official said.
Yokohama is Japan's largest port, handling 271 million deadweight tons of cargo in 2010, while Tokyo was No. 4 with 156 million, according to Lloyd's List Intelligence.
Hapag-Lloyd, the world's fifth-biggest container shipper, and container ship operator Claus-Peter Offen have stopped going to Tokyo and Yokohama for the time being.
Rival shipping company Hamburg Sued had suspended calls at the two ports but resumed trips there on Thursday.
The Singapore Shipping Association and industry officials said they were not aware of other companies diverting their vessels from Tokyo.
In China, officials detected what it said were "abnormal" radiation levels on a Japanese merchant ship entering the port at Xiamen in eastern Fujian province.
The report did not say how high the radiation levels were on the ship, which belongs to Mitsui O.S.K. Lines, or whether it had been turned away, Xinhua news agency reported.
WHO, the United Nation's International Maritime Organization, and the International Atomic Energy Agency have advised that maritime operations could continue as normal at seaports not damaged by the tsunami.
The March 11 disaster did less damage to Japan's port infrastructure than initially expected, with most of the supply chain problems located at railways, roads and factories.
All key Japanese seaports damaged by the March 11 disaster were now operational for recovery and reconstruction efforts.
"Fifteen of 15 ports in the afflicted area are usable. Multi-purpose piers are partly available, excluding Aomori port," the ministry said.
The estimated $300 billion damage from the quake and tsunami makes this the world's costliest natural disaster, dwarfing Japan's 1995 Kobe quake and Hurricane Katrina in New Orleans in 2005.
(Reporting by Randy Fabi in Singapore and Chikako Mogi in Tokyo; Editing by Ed Lane and Jo Winterbottom)