Local residents have in the past few days stocked up on iodine and dosimeters -- instruments that measure the amount of radiation -- prompting officials to warn residents against panic buying and excessive consumption of iodine drugs.

Radiation levels on Sakhalin, a large Pacific island close to Japan, were between 6 and 15 microroentgen per hour compared with a maximum accepted norm of 30 per hour, the regional emergencies ministry said.

As of 0700 GMT, radiation levels in the nearby Primorye region -- whose main city is Vladivostok radition,panic,did not change from the day before, averaging at 13 microroentgen, the regional emergencies ministry said on its website.

"There is no threat to life and health of people," it said.

Coast guard vessels off Sakhalin Island helped monitor the radiation, transmitting data to the special monitoring taskforce every two hours.

And in Vladivostok, located no more than 1,000 kilometres (600 miles) west of the Fukushima nuclear plant, molluscs were being used to assess the situation.

"Molluscs react to heavy metal ions which means they will sound an alarm if background radiation increases," local water company Primvodokanal said, adding it has been using this type of biomonitoring since last year.