The quake-hit Fukushima nuclear plant remained grave, a day after an explosion at a reactor.
Meanwhile, police have warned that the death toll in tsunami-hit Miyagi prefecture alone could exceed 10,000.
Japanese national broadcaster NHK says the total number of confirmed deaths now stands at 1,351.
Millions of survivors remain without electricity and authorities are stepping up relief efforts as the scale of the tragedy becomes clearer.
About 310,000 people have been evacuated to emergency shelters, many of them without power, Japanese broadcaster NHK reported.
Officials earlier announced that the number of troops helping with rescue work in the affected north-east region would be doubled to 100,000.
"The current situation of the earthquake, tsunami and the nuclear plants is in a way the most severe crisis in the past 65 years since World War II," Mr Kan said.
"Whether we Japanese can overcome this crisis depends on each of us.
"I strongly believe that we can get over this great earthquake and tsunami by joining together."
the shutting down of the Fukushima plant and other power stations meant that electricity supplies were limited.
He said that from Monday there would be a programme of rolling power cuts that would also affect water and gas supplies and some medical facilities. Speaking after Mr Kan, government spokesman Yukio Edano said that although seawater was being injected into reactor 3 at the Fukushima plant to cool it, gauges were not showing the water levels rising.
"We do not know what to make of this," he said.
On Saturday, a huge explosion blew apart the building housing reactor 1, where technicians had been venting steam to cool the reactor.
Cooling systems to both reactors failed after the 8.9 magnitude quake struck off the north-east coast.
About 170,000 people have been evacuated from a 20km (12.4 miles) area around the plant.
Japan's nuclear agency graded the situation at the Fukushima plant as a Level 4 incident on the International Nuclear and Radiological Events Scale (Ines).
Level 4 incidents normally involve at least one death from radiation, although no-one at the plant has died.
Meanwhile, Japan's nuclear energy agency has declared a state of emergency at a second nuclear facility, at Onagawa, after excessive radiation levels were recorded there.
Scores of ships and aircraft are struggling to reach areas worst-hit by the tsunami.
International rescue teams are also flying into Japan following an appeal by the government.
Stricken Miyagi prefecture includes the port of Minamisanriku which was mostly swept away by the tsunami.
But some survivors are being found. Japanese troops rescued a 60-year-old man who floated out to sea on the roof of his home after the tsunami hit.
A spokesman for Japan's military said Hiromitsu Shinkawa was pulled from the sea about 15km off the town of Minamisoma, in Fukushima prefecture, after he was spotted waving a red cloth.
Mr Shinkawa told his rescuers that the tsunami had hit as he and his wife returned home to gather some posessions after the earthquake, and that his wife was swept away.
|Source: BBC world news|