In the latest series of troubles to stall moves to stabilise the radiation leaking plant, work to connect power cables to No. 3 and No. 4 reactors was halted after smoke belched from the buildings of No. 2 and No. 3 reactors, said Tokyo Electric Power Co. (TEPCO), which operates the plant.
It said it will resume the operation tomorrow after observing the situation at the site.
Hidehiko Nishiyama, a spokesman for the Nuclear and Industrial Safety Agency was quoted as saying by Kyodo news agency that the causes of the smoke remain unknown and that work to resuscitate power and cooling systems at the troubled reactors will be delayed.
Yukiya Amano, the Director General of the International Atomic Energy Agency (IAEA) who made an emergency trip to Japan last week, was quoted as saying by Kyodo that the situation at the Fukushima plant "remains serious".
TEPCO said it had briefly evacuated its workers after grayish and blackish smoke was spotted at the No. 3 reactor around 3:55 p.m. above a pool storing spent nuclear fuel.
Even as the smoke stopped after 6 p.m., TEPCO later detected white smoke was rising through a crack in the roof of the building that houses the No. 2 reactor at around 6:20 p.m, the report said.
It forced the Tokyo Fire Department to halt spraying water for the day to cool the overheated fuel rods. It will suspend the operation until safety at the site is confirmed, it said.
Prime Minister Naoto Kan said slow but "steady progress" is being made in tackling the brewing crisis at the quake-hit power plant.
Kan also told a Cabinet-level emergency disaster headquarters meeting held at his office that he will gear up for reconstruction of the eastern Japan areas pummeled by the March 11 earthquake and ensuing tsunami.
Meanwhile, the death toll from the earthquake and tsunami that hit northeastern and eastern Japan and the number of those reported missing touched almost 22,000, the National Police Agency said.
The number of deaths reported in a total of 12 prefectures came to 8,649, while people reported by their relatives to be missing climbed to 13,262 in six prefectures. Police have identified about 4,080 bodies, including 2,990 returned to their families, the agency said.
Japan will monitor radiation levels in the Pacific Ocean near the Fukushima plant, where firefighters have been using seawater to cool reactor units, officials said.