Tokyo (CNN) -- A faint trail ofwhite smoke rose Tuesday over the damaged Fukushima Daiichi nuclear plant as workers continued efforts to restore power at the facility -- a key step that officials hope will allow them to bring cooling systems back online.
Japan's nuclear safety agency said it was not immediately clear why smoke was rising from the plant's No. 2 and No. 3 reactors. Tokyo Electric Power Company said in a statement that the smoke was decreasing and barely visible.
Officials temporarily evacuated workers from the plant Monday when smoke was spotted in the same area. But the agency said Tuesday that workers planned to continue efforts to restore power.
"This is going to be a two steps forward, one step back evolution," said Michael Friedlander, a former senior operator at three U.S. power plants who has been closely following the situation at the Fukushima Daiichi plant.
In terms of restoring power at the plant, workers are "on the verge of success," he told CNN's AC360.
But while work to reconnecting cooling systems continued, workers and firefighters resumed spraying water at the buildings housing the No. 3 reactor Tuesday afternoon, Tokyo Electric Power Co. said.
Crews also began using concrete pumps to pour water on the No. 4 reactor building, Kyodo News reported.
Workers have been scrambling to cool down fuel rods since a 9.0-magnitude earthquake and massive tsunami on March 11 knocked out cooling systems at the plant.
Police say the dual disaster has killed at least 9,079 people and left at least 12,645 missing, many of them killed as a wall of water rushed in following the quake.
Officials say some radiation has been released from the crippled plant since the quake and tsunami. And with the nuclear plant's six reactors in various states of disrepair, concerns have mounted over a potentially larger release of radioactive material from the facility, located about 240 kilometers (150 miles) north of Tokyo.
Officials said Tuesday that electrical cables had been laid to connect the No. 3 reactor and the neighboring No. 4 reactor with an outside power source.
That meant that power could now be funneled to all six of the plant's reactors for its cooling systems. But Tokyo Electric Power Company said Monday that electricity was still not moving to units No. 1 through No. 4 because the quake and tsunami had damaged numerous pumps and other gear. The company said spare parts were being brought in so that everything could work again.
The No. 3 reactor has been the top priority for authorities trying to contain damage to the plant and stave off a possible meltdown. Its fuel includes a small percentage of plutonium mixed with the uranium in its fuel rods, which experts say could cause more harm than regular uranium fuels in the event of a meltdown.
Hidehiko Nishiyama of Japan's Nuclear and Industrial Agency said there was no evident explosion, spike in radiation or injuries at the No. 3 reactor Monday. The smoke came from the building's southeastern side, where the reactor's spent nuclear fuel pool is located, but the origin of the smoke at either reactor was unknown.
A spent fuel pool is also a concern in the building housing the No. 4 reactor.
The coolant pools contain used fuel rods that contain radioactive material and still generate high amounts of heat. Authorities have been working to keep them full to prevent the rods from being exposed and releasing radiation.
"The crisis has still not been resolved, and the situation at the Fukushima Daiichi nuclear power plant remains very serious," Yukiya Amano, the director-general of the International Atomic Energy Agency told the UN watchdog's board of governors Monday after a visit to the site.
On the other hand, Amano told reporters, rising pressure inside the containment unit at reactor No. 3, a concern from the weekend, was down and power had been restored to some of the reactors.
About 660 workers were at the site Tuesday, Tokyo Electric said. About 330 of those were employees of the power company.
Authorities said potential food contamination remains a concern.
The Japanese government has banned the sale of raw milk from Fukushima Prefecture, where the plant is located, and prohibited the sale of spinach from neighboring Ibaraki Prefecture after finding levels of radioactive iodine and cesium higher than government standards, the country's health ministry reported.
And officials in Fukushima halted the distribution of locally grown vegetables outside the prefecture.
High levels of radioactive substances have also been found in seawater near the plant, Tokyo Electric said Tuesday, adding that the results do not represent a threat to human health.
"There should be no immediate health impact. If this situation continues for a long period of time, some impact can occur," Chief Cabinet Secretary Yukio Edano told reporters.
