Minoru Yoshida, 63, told Japanese broadcaster NHK that he was on the first floor of unit 4 when the quake hit.
"The building shook sideways and the lights went out. I held onto a post because I thought the switchboard was going to collapse. I think there were about 200 workers on the first floor. However because of the dust in the air, I could not see very well and the fire drills were going off," Yoshida told NHK.
Another worker was standing between unit 3 and unit 4 dismantling construction scaffolding, NHK reported.
"I thought the building would be stronger. I would have never imagined the building would turn out the way it did," he said.
Experts say Japan never planned for the plants to handle a 9.0 earthquake followed by a tsunami.
The problems at the Fukushima Daiichi plant have left engineers concerned containment vessels may be damaged and leaking.
Yukiya Amano, the head of the U.N's International Atomic Energy Agency, characterized the struggle to fix the problems as a race against time.
"We see it as an extremely serious accident," Amano said. "This is not something that just Japan should deal with, and people of the entire world should cooperate with Japan and the people in the disaster areas."
Despite the rise in rating, a U.S. official said that the worst-case scenario of a nuclear meltdown should never be encountered as long as efforts to contain the crisis continue.
"I am cautiously optimistic that we're progressing in that regard based on what we've seen, and the restoration of power and the efforts that they've made to add water, both, you know, from the outside and the top of these reactors," said Adm. Robert Willard, the head of U.S. Pacific Command, who has overall responsibility for the U.S. relief effort in Japan.
Willard, who briefed reporters from his headquarters in Hawaii, will travel Saturday to Japan to meet with senior military officials to see what more the U.S. can offer. The Japanese military, he said, was just beginning to ramp up its operations and only now is looking at some of the "long list" of offers of assistance made by the U.S. military.
The U.S. has already given the Japanese high-pressure pumps to keep water flowing to the reactor.
Nearly 140 additional Japanese specialist firefighters volunteered in Tokyo to help the mission on Friday. Each team member got a personal farewell from Tokyo Fire Department Chief Yuji Arai.
"We expect a lot of difficulties with the mission we have been given," he said. "I think it is really a dangerous assignment. ... The reputation of Japan and the lives of many people rest on your actions."
Across the nation, the Japanese bowed their heads in a moment of silence today for all those lost and devastated by the quake and tsunami.
Japanese Prime Minister also attempted to raise the spirits of his beleaguered nation a week after a 9.0-magnitude earthquake and tsunami killed 6,900 and left 10,354 still missing.
"We will rebuild Japan from scratch. We must all share this resolve," he said in a televised address.
It could take weeks to get enough water on the reactors to cool them adequately, according to Gregory Jaczko, chairman of the Nuclear Regulatory Commission. He called the situation "dynamic, difficult, and even tragic."