Nissan Motor said Friday it would monitor all its vehicles made in Japan for radioactivity, amid international concern over efforts to avert a nuclear catastrophe at a stricken atomic plant.

"We will continue to implement all appropriate measures to reassure the public that all products from our company remain within globally accepted safety standards," the company said in a statement.

The testing will continue "until we are confident that any risk of contamination is completely removed," the automaker said.

Attempts are being made by Japan's Self-Defence Forces to douse fuel rods and prevent a calamitous radiation release at the Fukushima No. 1 power station.

Levels of radiation there have fluctuated wildly after the plant 250 kilometres (155 miles) northeast of Tokyo suffered critical damage from Japan's biggest ever earthquake last week and the devastating tsunami it unleashed.

The government has set a 20-kilometre exclusion zone and told those living between it and 30 kilometres from the plant to stay indoors as hourly radiation levels in the some nearby areas spike.

The twin disasters knocked out the cooling systems, sparking a series of explosions and fires. Authorities have since raced to keep the fuel rods inside reactors and containment pools submerged under water.

If they are exposed to air, they could degrade further and emit even more dangerous radioactive material.