Prime Minister Naoto Kan said slow but "steady progress" is being made in tackling the brewing crisis at the quake-hit Fukushima nuclear power plant.
"Grayish smoke was seen coming out from a building that houses the No.3 reactor of the troubled atomic unit and Tokyo Electric Power Co., which runs the unit said that workers had been "temporarily" asked to evacuate.
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 Mar 11 earthquake and ensuing tsunami, the Kyodo reported.
Meanwhile, the death toll from the Mar 11 earthquake and tsunami that hit northeastern and eastern Japan and the number of those reported missing touched to near 22,000 as of today, the National Police Agency said, Kyodo reported.
After the smoke was spotted at the southeast of the building around 3:55 p.m., TEPCO said it had temporarily evacuated its workers from the site as it assessed the situation. The amount of smoke later decreased, TEPCO added.
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.
Following a magnitude 9.0 quake and ensuing tsunami on March 11, cooling functions of the No. 3 reactor were lost and its core is believed to have partially melted.
At present, coolant water is pumped into the reactor and a pool for spent nuclear fuel. The roof and upper walls of the building that houses the No. 3 reactor were blown off by a hydrogen explosion last week.
On Sunday, pressure in the No. 3 reactor's containment vessel temporarily rose, but it later stabilized.
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.
A total of about 340,000 evacuees, including those who fled from the vicinity of the troubled nuclear reactors in Fukushima Prefecture, are now staying at some 2,070 shelters set up by 16 prefectures. .