The French government and Czech military have evacuated some of their citizens from Japan on special flights and Britain is planning the same, as international worries grew about health risks from Japan's leaking nuclear plants.

The United States has authorized the first evacuations of Americans out of Japan, warning U.S. citizens to defer all non-essential travel to any part of the country as unpredictable weather and wind conditions risked spreading radioactive contamination.

Japanese authorities are trying to cool down damaged nuclear reactors and pools of spent fuel at the Fukushima Dai-chi plant, damaged by last week's devastating earthquake and tsunami.

The radiation threat appears so far limited. Risks from possible radiation exposure remain greatest for the workers scrambling to cool the reactors. Those who have been evacuated from the site are considered safe, as are the 39 million people who live in the greater Tokyo region.

Still, the French Foreign Ministry said in a statement Thursday that it "strongly advises against trips to Japan" and urges French citizens in the Tokyo region to head south or return to France.

Two French government planes are bringing home French people who want to leave Japan. One left Tokyo on Thursday for Seoul, with 241 people aboard.

Air France has also increased the capacity of its twice-daily flights in and out of Tokyo.

France's nuclear manufacturer Areva and utility EDF sent a plane on Thursday with 100 tons of boric acid to help contain radiation leaks, 10,000 protective uniforms, 20,000 pairs of gloves and 3000 protective masks. France is a leading nuclear energy producer and has pledged to help Japanese authorities deal with their nuclear crisis.

Two Czech military planes landed in Prague on Thursday morning after evacuating 106 people from Japan, mostly Czechs but also several nationals of Poland, Slovakia, Bulgaria and Korea. Also onboard were 41 members of the Czech Philharmonic Orchestra that had been touring Japan since March 6, as well as 11 children.

Germany announced it has temporarily transferred its embassy from Tokyo to Osaka, in line with the foreign ministry's travel advisory issued Wednesday that urges its citizens still in the country to leave the Tokyo area for Osaka or leave Japan altogether.

Britain is advising its nationals in Tokyo and to the north of the city to consider leaving the area, and the Foreign Office has decided to organize charter flights from Tokyo to Hong Kong to supplement commercially available options for those wishing to leave Japan. Spain said it was considering all options.

Some countries were more measured in their reactions.

"If you are in the larger Tokyo area, we urge you to consider to move away, southward or out. This is completely up to you," Denmark's Ambassador Franz-Michael Skjold Mellbin said Thursday in a live webcast transmission from the Danish Embassy in Tokyo.

"The worst thing may actually be to join the panic situation and get outside, get stuck for three days outside Tokyo en route south and be exposed to unnecessary high levels of radiation."

Skjold Mellbin said the Danish Embassy would remain in Tokyo even with several meltdowns.

Italy is considering a special evacuation flight for Italians in special need, such as pregnant women, families with young children, those who might be ill or who just couldn't afford commercial flights. Switzerland is also considering charter flights if needed.

The Swedish government is working on a plan to help its citizens leave Japan, and is currently looking at air travel capacity.

In Washington, senior State Department official Patrick Kennedy said Wednesday that chartered planes will be brought in to help private American citizens wishing to leave.

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Associated Press writers Cassandra Vinograd in London, Jan M. Olsen from Copenhagen, Karel Janicek in Prague, Louise Nordstrom in Stockholm, Frances D'Emilio in Rome and John Heilprin in Geneva contributed to this report.