Japan's government is on "maximum alert" over the damaged nuclear plant, says Japanese Prime Minister Naoto Kan.
Workers are still trying to cool down the nuclear reactors, to help stop any potentially dangerous leaks.
Toxic chemical plutonium has been found in the soil at the plant. But officials say it's not enough to threaten humans.
Highly radioactive water has also been discovered outside the nuclear buildings for the first time. Work is now on to stop it seeping into the sea.
Low levels of radioactive material thought to be from Japan have been detected in the air in Glasgow, Scotland.
But experts say it's so tiny, it's nothing to be worried about.
Radioactivity has also been recorded in the air by officials in China, South Korea and America. But again, none of it is believed to be high enough to be a worry.