The temperature in reactor 4 has increased from Thursday, the official said, and the fuel rods -- which are supposed to be housed in a steel container surrounded by concrete -- are surrounded only by steel because the concrete has blown away.
Limited progress has been made in restoring power to the reactors, said the official. Reactor 2 is currently the only reactor to have a live power line connected to it and Japanese officials hope they can connect lines in more reactors over the weekend. The water pumps the U.S. sent require power to operate and will not be functional until electricity is restored.
The U.S. and Japan continue to disagree about whether there is water in cooling pools at reactors 3 and 4. Images from a Japanese helicopter flyover made it appear there was some, but the U.S. Nuclear Regulatory Commission said it is still not certain, given that the heat level remains extremely high.
In light of the disagreement Rep. Edward Markey, D-Mass., the top Democrat on the House Natural Resources Committee asked the Nuclear Regulatory Commission to provide daily reports and analysis of the situation.
The U.S. official also told ABC News that the situation remains very serious and that if everything went well over the course of the next few weeks, it would just go from being an emergency to remaining very dangerous.
Earlier today, Japanese officials raised the nuclear crisis level at the troubled plant, putting the ongoing battle to cool the damaged nuclear reactors and spent fuel ponds on par with the accident at Three Mile Island in 1979.
The rating of the crisis was raised to a 5 from a 4 on a scale used by the International Atomic Energy Agency. That's just two levels below Chernobyl, which was rated a 7, the highest possible level on the international scale set by the International Atomic Energy Agency. A 4 connotes a radiation problem with local effects; a 5 means its effects are wider and a 7 means the effects are seen, at least at some level, globally.
"It's a race against time. At a certain point, they might have to evacuate and then the whole reactor accident is in freefall," said theoretical physicist Dr. Michio Kaku. "I think the credibility of the utility [Tokyo Electric Power Co.] has melted down. ... Pictures don't lie."
The latest pictures of the plant show smoke billowing from the crippled nuclear reactors and spent fuel ponds as Japanese military and emergency crews desperately try to prevent a nuclear meltdown.
"This steam contains radioactive seasoning. ... This cloud is now going over northern Japan. It's being picked up in Tokyo now in small levels," Kaku said. "This whole area [around the plant] is a near deadly radiation field."
Out of six reactor units on Fukushima Daiichi plant, four have caught fire, exploded or suffered partial meltdowns in the past week. Water levels in the pools where used fuel rods are stored are believed to be dangerously low.
Two men working at the nuclear plant on the day the 9.0 earthquake and tsunami struck Japan have spoken out on the chaos that erupted the day of the disaster.
Minoru Yoshida, 63, told Japanese broadcaster NHK that he was on the first floor of unit 4 when the quake hit.