Bulgarian scientists have tried to assuage fears that radiation winds could reach the country after Japan nuclear plant blasts, ruling out the very possibility of such a scenario.

"Talk that Bulgaria may be affected by radiation waves following the explosions at the Japanese quake-stricken Fukushima Daiichi nuclear plant is just absurd," Valeri Spiridonov, deputy head of the National Institute for Meteorology and Hydrology with the Bulgarian Academy of Sciences, said on Tuesday.

If the effort to cool the nuclear fuel inside the reactor fails completely, which is the worst-case and very unlikely a scenario, the resulting release of radiation could not reach Bulgaria because the winds are heading west-eastwards, according to Spiridonov.

"In case of a possible release of radiation into the atmosphere at an altitude of over 1000 meters, the radioactive particles will move towards the Pacific Ocean and America," he explained.

"Even if they happen to head for Bulgaria, influenced by unusual cyclones, they will fail to reach the country. It is just impossible that they will manage to cross the whole of Siberia only to fall over Bulgaria."

The Japanese authorities said on Tuesday that the radiation crisis at the nuclear plant which was damaged in Friday's earthquake and tsunami is worsening, and levels are now high enough to affect human health.

The danger has been caused by a new explosion at one of the reactors in the Fukushima plant, followed by a fire. The operator says meltdown is now possible.