The prime minister said it was the nation's worst crisis since World War II.
Nuclear plant operators worked frantically to try to keep temperatures down in several reactors crippled by the earthquake and tsunami, wrecking at least two by dumping sea water into them in last-ditch efforts to avoid meltdowns.
Officials warned of a second explosion but said it would not pose a health threat.
Near-freezing temperatures compounded the misery of survivors along hundreds of kilometres of the northeastern coast, which was battered by the tsunami that smashed inland with breathtaking fury.
Rescuers pulled bodies from mud-covered jumbles of wrecked houses, shattered tree trunks, twisted cars and tangled power lines while survivors examined the ruined remains.
One rare bit of good news was the rescue of a 60-year-old man swept away by the tsunami who clung to the roof of his house for two days before a military vessel spotted him waving a red cloth about 15km offshore.
The death toll surged because of a report from Miyagi, one of the three hardest hit states. The police chief told disaster relief officials more than 10,000 people were killed, police spokesman Go Sugawara told The Associated Press.
That was an estimate - only 400 people have been confirmed dead in Miyagi, which has a population of 2.3 million.
According to officials, more than 1400 people were confirmed dead and more than 1000 were missing. Another 1700 were injured.
For Japan, one of the world's leading economies with an ultramodern infrastructure, the disasters resulted in almost unimaginable deprivation.
Hundreds of thousands of hungry survivors huddled in darkened emergency centres that were cut off from rescuers, aid and electricity.
At least 1.4 million households had gone without water since the quake struck and about 1.9 million households were without electricity.
While the government doubled the number of soldiers deployed in the aid effort to 100,000 and sent 120,000 blankets, 120,000 bottles of water, 110,000 litres of fuel plus food to the affected areas, Prime Minister Naoto Kan said electricity would take days to restore.
In the meantime, he said, electricity would be rationed with rolling blackouts to several cities, including Tokyo.
"This is Japan's most severe crisis since the war ended 65 years ago," Kan told reporters, adding that Japan's future would be decided by its response.
In Rikuzentakata, a port city of over 20,000 virtually wiped out by the tsunami, Etsuko Koyama escaped the water rushing through the third floor of her home but lost her grip on her daughter's hand and has not found her.
"I haven't given up hope yet," Koyama told public broadcaster NHK, wiping tears from her eyes. "I saved myself, but I couldn't save my daughter."
A young man described what ran through his mind before he escaped in a separate rescue.
"I thought to myself, ah, this is how I will die," Tatsuro Ishikawa, his face bruised and cut, told NHK as he sat in striped hospital pajamas.
Japanese officials yesterday raised their estimate of the quake's magnitude to 9.0, a notch above the U.S. Geological Survey's reading of 8.9. Either way, it was the strongest quake ever recorded in Japan, which lies on a seismically active arc.
A volcano on the southern island of Kyushu - hundreds of kilometres from the quake' epicenter - resumed spewing ash and rock after a couple of quiet weeks, Japan's weather agency said.
Dozens of countries have offered assistance. Two US aircraft carrier groups were off Japan's coast and ready to help. Helicopters were flying from one of the carriers, the USS Ronald Reagan, delivering food and water in Miyagi.
Two other US rescue teams of 72 personnel each and rescue dogs arrived Sunday, as did a five-dog team from Singapore.
Still, large areas of the countryside remained surrounded by water and unreachable. Fuel stations were closed, though at some, cars waited in lines hundreds of vehicles long.
The United States and a several countries in Europe urged their citizens to avoid travel to Japan. France took the added step of suggesting people leave Tokyo in case radiation reached the city.
Community after community traced the vast extent of the devastation.
In the town of Minamisanrikucho, 10,000 people - nearly two-thirds of the population - have not been heard from since the tsunami wiped it out, a government spokesman said.
NHK showed only a couple concrete structures still standing, and the bottom three floors of those buildings gutted. One of the few standing was a hospital, and a worker told NHK that hospital staff rescued about a third of the patients.
In the hard-hit port city of Sendai, firefighters with wooden picks dug through a devastated neighborhood.
One of them yelled: "A corpse." Inside a house, he had found the body of a gray-haired woman under a blanket.
A few minutes later, the firefighters spotted another - that of a man in black fleece jacket and pants, crumpled in a partial fetal position at the bottom of a wooden stairwell.
From outside, while the top of the house seemed almost untouched, the first floor where the body was had been inundated. A minivan lay embedded in one outer wall, which had been ripped away, pulverized beside a mangled bicycle.
The man's neighbor, 24-year-old Ayumi Osuga, dug through the remains of her own house, her white mittens covered by dark mud.
Osuga said she had been practicing origami, the Japanese art of folding paper into figures, with her three children when the quake stuck.
She recalled her husband's shouted warning from outside: "'GET OUT OF THERE NOW!'"
She gathered her children - aged 2 to 6 - and fled in her car to higher ground with her husband. They spent the night in a hilltop home belonging to her husband's family about 20km away.
"My family, my children. We are lucky to be alive," she said.
"I have come to realise what is important in life," Osuga said, nervously flicking ashes from a cigarette onto the rubble at her feet as a giant column of black smoke billowed in the distance.
As night fell and temperatures dropped to freezing in Sendai, people who had slept in underpasses or offices the past two nights gathered for warmth in community centres, schools and City Hall.
At a large refinery on the outskirts of the city, 30m -high bright orange flames rose in the air, spitting out dark plumes of smoke. The facility has been burning since Friday.
The fire's roar could be heard from afar. Smoke burned the eyes and throat, and a gaseous stench hung in the air.
In the small town of Tagajo, also near Sendai, dazed residents roamed streets cluttered with smashed cars, broken homes and twisted metal.
Residents said the water surged in and quickly rose higher than the first floor of buildings.
At Sengen General Hospital, the staff worked feverishly to haul bedridden patients up the stairs one at a time. With the halls now dark, those who can leave have gone to the local community centre.
"There is still no water or power, and we've got some very sick people in here," said hospital official Ikuro Matsumoto.
Police cars drove slowly through the town and warned residents through loudspeakers to seek higher ground, but most simply stood and watched them pass.
In the town of Iwaki, there was no electricity, stores were closed and residents left as food and fuel supplies dwindled. Local police took in about 90 people and gave them blankets and rice balls, but there was no sign of government or military aid trucks.
