Steam was seen rising from Japan's troubled Fukushima Daiichi plant early Thursday as workers continue to battle a potential nuclear meltdown following last week's devastating earthquake and tsunami.

While Tokyo Electric Power Co. resumed work in the morning morning to restore power and cooling functions at the plant, steam was seen rising from the 4 reactors, according to Japan's NHK news service, notably marking the first time steam has been seen out of reactor No. 1.

The power company did say that the black smoke seen rising from the No.3 reactor building on Wednesday was no longer visible as of 6:00 AM Thursday, however.

There are some positive developments related to the availability of electrical power ... although the overall situation remains of serious concern, Graham Andrew, a senior official of the International Atomic Energy Agency (IAEA), told a news conference.

The plant, battered by a 9.0 magnitude earthquake and tsunami that has left 23,000 people dead or missing, has still not been brought under control, and workers were forced away from the complex when black smoke began rising from one of its six reactors.

The first official estimate puts the overall costs of the disaster at more than $300 billion, making it the world's costliest natural disaster. Already some countries have started blocking imports of produce from Japan, fearful of radiation contamination.