The French government said on Wednesday that Japan was losing control of the situation at the Fukushima nuclear power plant and urged its nationals in Tokyo to leave the country or head to southern Japan.
The government has asked national carrier Air France to increase capacity on its flights between Tokyo and Paris to accommodate any additional demand from French citizens wanting to leave the Japanese capital.
Industry Minister Eric Besson said the situation at the Fukushima plant, some 240 km (150 miles) north of Tokyo, appeared to be getting out of control.
"Let's not beat about the bush. They have visibly lost the essential of control (of the situation). That is our analysis, in any case, it's not what they are saying," Besson told BFM television.
Environment Minister Nathalie Kosciusko-Morizet branded the situation in Japan a "catastrophe" and said the latest information on Wednesday "does not lead to optimism".
"We recommend that all French citizens who do not have a good reason to stay in Tokyo either take a plane or, if they absolutely insist on staying, head south," Kosciusko-Morizet said. She noted there was no official evacuation order.
A government plane returning from taking French rescue workers to Japan was due to arrive on Wednesday at Paris's Roissy-Charles de Gaulle airport carrying 300 French citizens -- mainly priority cases such as children and pregnant women.
Air France has increased the number of seats available on its Paris-Toyko route to 944 a day, from 871 normally, by using two Boeing 777 planes from Tuesday until Sunday.
"It seems that corresponds to the demand," Kosciusko-Morizet said.
Prime Minister Francois Fillon has said that only around 2,000 French citizens remain in the Tokyo area, down from 5,000 normally. Some 600 French people were believed to be in the Sendai region, the worst hit by Friday's earthquake and tsunami.