PASSENGERS flying from Phuket and Bangkok to airports in Japan will be offered potassium iodide tablets from Thursday as a precaution against exposure to nuclear radiation.

Thailand's Public Health department has 15,000 doses - 10,000 of 130 mg for adults and 5000 of 65mg for children - to give to people choosing to fly to Japan.

While radiation levels following the blasts and fires at Fukushima nuclear plant remain difficult to guage - and so far officially not a threat - levels of disquiet have risen alarmingly.

The Thai precaution will do nothing to ease that disquiet. The precaution comes as Thailand's official travel alert, in line with those of many other nations, warns against non-essential travel to Japan.

The government's National News Bureau says more than 70 percent of package tour bookings to Japan for March to May have been canceled.

Foreign Minister Kasit Piromya said that about 300 Thais live in Sendai prefecture of Japan, which was badly struck by Friday's tsunami. About 100 have left the area, but 200 others were still out of contact.

Thailand's plan to implement nuclear power over 20 years has been put on hold as governments around the world see the images from Japan and opt to take a safety first approach.

Potassium iodide protects the thyroid gland against cancer by blocking absorption of radioactive iodine.

According to news agency reports, supplies in Japan have become short, and panic buying has been reported as far away as North America.