Update: U.S. Embassy personel in Tokyo have been moved to an offsite location (see bottom)
Not sure why the media and government of Japan isn't calling a spade a spade here. All the news I've been hearing has been playing this down. It exploded as can be seen here.
According to Youtube this is Reactor One which appears to have been completely destroyed.
Here are the Fema safety guidelines for anyone near a meltdown. I would imagine the wind might carry the radioactivity a good distance as well.
Business Standard confirms a meltdown.
..."The plant is experiencing a nuclear meltdown," Japanese nuclear scientists confirmed, after Prime Minister Naoto Kan visited the site in a helicopter early today.
Reports said the main building of the plant housing the reactor as well as the outer walls were blown away in the high intensity explosion which occurred at 3.30 pm local time (1200 IST) as the cooling water levels dropped alarmingly through evaporation after the quake had damaged the main plant.
"The loss of cooling water is leading to a meltdown of the reactor," Jiji Press reported.
TV footage showed smoke billowing from the site and reported that the reactor building had been destroyed. The channels and public broadcasters warned nearby residents to turn off air conditioners and not to drink tap water.
People going outside were told to avoid exposing their skins and to cover faces with masks and wet towels.
Kyodo quoting police said that another nuclear plant adjacent to the one which exploded was also malfunctioning with the radiation level reaching almost 1000 times the normal level...
United States delivers coolant to quake-hit Japan's nuclear plant
..."We just had our Air Force assets in Japan transport some really important coolant to one of the nuclear plants," Secretary of State Hillary Clinton announced yesterday, as Tokyo declared a state of emergency for five of its nuclear reactors at two atomic power plants in northeastern coast of Japan, where an 8.9-magnitude quake struck yesterday...
mmm...seems that coolant really did the job there.
Obama said he has dispatched a second ship to the region for possible relief and rescue operation. "We currently have an aircraft carrier in Japan, and another is on its way. We also have a ship en route to the Marianas Islands to assist as needed," he said.
"The Defence Department is working to account for all our military personnel in Japan," he said.
The US embassy personnel in Tokyo have moved to an offsite location.
The State Department is working to account for and assist all American citizens who are in the country.