Three evacuees have been exposed to radiation, but have not shown signs of illness, a disaster official told The Associated Press.
Japanese authorities say they have plans to distribute iodine to residents in the area around both the Fukushima Daiichi and nearby Fukushima Daini plants.
Meanwhile, Japanese authorities are racing to rescue those trapped in the rubble after an8.9 magnitude earthquake and a tsunami left hundreds dead and a nuclear reactor on the verge of a possible of meltdown.
Prime Minister Naoto Kan said he dispatched 50,000 troops for recovery efforts as powerful aftershocks continue to rattle the region.
Tsunami survivors were plucked by helicopters and from rooftops, but hundreds more along the 1,300-mile stretch of coastline are waiting to be rescued. There are 200,000 people living in temporary shelters after being evacuated to higher ground and more than 1 million households are without water. Five million households lack electricity.
The earthquake, the fifth largest in recorded history and the largest ever to hit Japan, struck about 2:46 p.m. local time.
It triggered a tsunami that unleashed a menacing stew of debris with objects as large as ships, cars and houses coursing over the countryside and into towns, crushing buildings and everything in its path. Eerily, fires burned in the watery mess as it flowed along.
Entire villages were swept away and four bullet trains with an unknown number of people onboard lost contact with rail operators Friday, according to the Kyodo News Agency.
Hours after the buildings stopped shaking, fires still burned and Tokyo remained largely paralyzed with phone and train service halted on Friday. Four million buildings were without power.
Many in Tokyo spent the night in their cars trying to get home because the highways were closed and cars clogged the city's streets.
Store shelves were stripped bare by shoppers and thousands more spent the night in their offices.
It was harder to assess damage outside the capital because of cut phone communications.
Much of the town of Kesennuma near Miyagi, burned during the night with no apparent hope of being extinguished, public broadcaster NHK said.
Japan's coast guard was searching for 80 dock workers on a ship that was swept away from a shipyard in Miyagi.
President Obama called the tsunami "catastrophic" and said help was coming. The United States has one aircraft carrier in Japan and another is on the way, and a ship is also en route to Marianas Islands for assistance, Obama said.
A USAID Disaster Urban Search and Rescue teams of more than 150 people are headed to Japan to assist in the rescue effort. The Pentagon is sending some P-3 Orion maritime surveillance aircrafts to support the Japanese government by providing aerial reconnaissance over quake-damaged areas.
So far there are no reports of American fatalities in Japan, but anxious posts on Facebook by Americans living there reveal the devastation in the hard-hit Sendai area.
Randy Castle, an American working in Japan, said his hotel lobby was full of people overnight who couldn't make it home from work.
"It started and it lasted a good five minutes, lots of shaking and very scary. I'm on the 11th floor, just down the street from the Tokyo tower," Castle said.
The Tokyo tower, a famed landmark in Japan, now stands bent.