Japan's prime minister said Friday that the situation at the plant remains, "grave and serious." Prime Minister Naoto Kan also thanked utility workers, firefighters and military personnel for "risking their lives" to cool the overheated facility.
Work at the complex has stopped while officials investigate whether the core in one reactor has actually been breached. That could mean more serious radioactive contamination and could create long delays in work to contain other radiation leaks.
Officials said the possible breach was discovered when two workers suffered skin burns when water splashed over their protective boots.
Kan apologized to farmers and business owners for the toll the radiation has had on their livelihoods. Radioactive traces have been found in milk, seawater and 11 kinds of vegetables grown near the plant.
The alarm Friday comes on a day marking two weeks since the magnitude-9.0 quake triggered a tsunami that enveloped cities along the northeast coast and knocked out the Fukushima reactor's cooling system.
The official death toll has surpassed 10,000 and more than 17,400 people are listed as missing. The final number of dead was expected to be more than18,000.
The Associated Press contributed to this report.