Updated March 21st 20:05
Currently, World Health Organizaiton are NOT advising travel restriction to Japan.
Following information are gathered by Hikaru Kitamura
Organizer of Japan earthquake 東北地方太平洋沖地震 (http://www.facebook.com/?sk=group_116365381773884)
WHO Spokesperson Gregory Hartl commented on Japan's situation regarding radiation, "There is little public danger." It is very unlikely that food sold & exported are affe...cted by the radiation of the Fukushima Power Plant I, countries checking radiation levels of food imported from Japan as well as ordering their people to leave Japan are overreacting. [This means people being checked is also unnecessary.]
UNifeed: GENEVA / JAPAN HEALTH UPDATE [video available]
Quotation from another WHO webpage:
"17 March 2011 -- WHO is cautioning people concerned about the radiation issues in Japan against self-medicating with potassium iodide or taking products containing iodine. The advice follows reports of people using these substances in response to radiation leaks from nuclear plants in Japan. Potassium iodide should only be taken when there is a clear public health recommendation to do so."
WHO | Japan earthquake and tsunami
WHO has also made a Japanese FAQ to provide proper knowledge about radiation.
WKC | WHO Centre for Health Development
From NHK (around 22:00, March 20): The International Atomic Energy Agency (IAEA) Director General Amano was concerned that rumors were spreading out in the world, various countries worrying that radiation in Japan will affect them. He mentioned that ...the information provided is not enough, that Japan should collaborate with the IAEA and report point by point, several countries (organizations) working on together will be better. IAEA will monitor radiation levels in Tokyo and other areas in the Kanto region, separately from Japanese institutions.
Details of Amano's visit to Japan are available on the IAEA website.
Japanese Prime Minister Assures Director General of Increased Information Exchange
http://www.iaea.org/newscenter/news/2011/japan-visit.htmlLatest report of the current situation of the Fukushima nuclear power plants by the IAEA has been published online at March 19 2011, 21:00 JST (Japan Standard Time, UTC+9).
IAEA Update on Japan Earthquake