Work to stabilize the damaged reactors at the Fukushima Daiichi nuclear power plant was temporarily halted early Wednesday because radiation leaking from the units made the situation unsafe, Japanese officials said.
Several hours after work was halted, officials were preparing to return to work but it was unclear whether workers were able to enter the plant, the Associated Press reported.
Radiation levels started to rise sharply after steam was seen escaping from unit 3 at the plant, which was damaged first by the 9.0 earthquake and tsunami that struck Japan Friday, and then by an explosion in the reactor.
There have been explosions in two other reactors at the plant, and two fires at a fourth unit, which was being used as a storage facility for radioactive material.
A Japanese government official also indicated for the first time that the containment vessels of all three of the reactors at the plant that exploded may be leaking, raising worries of dangerous radiation leaks.
The release of steam and work stoppage came after firefighters were able to put out a fire at unit 4 at the plant.
The International Atomic Energy Agency said Tuesday that radiation dose rates of up to 400 millisievert (mSv) per hour had been reported at the Fukushima plant site immediately following one of the explosions. A typical chest X-ray exposes an individual to about 0.02 mSv.
But after the steam was observed escaping from unit 3, radiation levels rose sharply, a government spokesman said.
Chief Cabinet Secretary Yukio Edano said there was a reading of 1,000 millisieverts, before the dose level began falling again to 600-800 millisieverts per hour, which is still considered unsafe.
"So the workers cannot carry out even minimal work at the plant now," Edano said. "Because of the radiation risk, we are on standby."
To learn more about nuclear radiation, click here.
Japan's Self-Defense Forces had attemped by helicopter to put water on unit 3 but radiation levels were unsafe to complete the mission according to NHK and the Kyodo news agency.
Also on Wednesday, in a rare address, Japan's Emperor Akihito expressed his concerns with the nuclear crisis and gave his condolences for the victims and told the country "not to give up" on national television, the Associated press reported.
Japanese Prime Minister Naoto Kan urged those living 12 to 19 miles around the plant (20-30 km) to stay indoors. The 140,000 people living within 12 miles of the plant have been evacuated. So far, 150 people from that area have tested positive for exposure to radiation.
"Please do not go outside. Please stay indoors. Please close windows and make your homes airtight. Don't turn on ventilators. Please hang your laundry indoors," Chief Cabinet Secretary Yukio Edano said to the residents in the danger zone. "These are figures that potentially affect health. There is no mistake about that."
Heeding the government's word to evacuate, cars jammed highways and waited in lines four lanes wide to get gas. Aircraft were also affected by the damaged nuclear plant. The Japanese Transport Ministry imposed a 19 mile no-fly zone near the facility, allowing only aircraft involved in relief efforts to be exempt from the restriction.