Japanese government officials said Saturday evening that the explosion did not damage the nuclear containment structure at the Fukushima Daiichi plant's Unit 1, and they conveyed an initial sense that a widespread radioactive leak could be avoided.

As nuclear workers scrambled to bring temperatures at the reactor to safe levels by filling the container with sea water, Japan was already dealing with the previous day's twinned disasters -- an 8.9-magnitude earthquake and a resulting tsunami.

Japan's government on Saturday broadened its rescue efforts, searching for survivors along a decimated swath of the Pacific coast. But in many places rescuers found only the remnants of places that once were.

Roughly 9,500 in Minamisanriku -- a town of 17,000 in Miyagi Prefecture -- remain missing or unaccounted for, according to the Kyodo news agency, citing local government officials. As of Saturday evening, police said that 621 were confirmed dead, with thousands more missing. More than 210,000 had been evacuated.

In the areas north of Tokyo, closest to the epicenter of Friday's earthquake, eyewitnesses described entire neighborhoods that have disappeared after being swallowed and chewed up by a massive tsunami wave. Attempts to reach those stranded, trapped or short on supplies were complicated by damage to the roads and rail lines.

The U.S. Geological Survey reported dozens of additional aftershocks off the coast of Japan's main Honshu Island, including a 6.1-magnitude quake. Just after 10 p.m. local time a 6.4 aftershock hit 50 miles away from Fukushima Prefecture, shaking buildings as far away as Tokyo.

Given the continued communication problems with towns in the North and scant initial information about the implications of the nuclear plant explosion, Japan on Saturday tried at once to piece together what had happened and what was happening still.

For several hours Saturday afternoon, those in Tokyo saw only the images played on a loop by national television broadcasters. Smoke billowed from the Fukushima Daiichi nuclear plant, and government officials warned those in the area to stay indoors -- or cover their mouths with wet cloths when walking outside. Even in Tokyo, frightened consumers rushed stores, stacking up on water and food.

Meantime, attempts to map out the damage caused a day earlier were only beginning as Japan dispatched 50,000 troops to the disaster zone. The coastal town of Rikuzentakata, in Iwate Prefecture, was entirely submerged by water, according to local authorities. One TV reporter arrived at Iwaki, in Fukushima Prefecture, and reported that the entire town was gone. A hospital in Iwanuma had written "SOS" -- in English -- on the roof. A derailed train in Miyagi Prefecture, closest to the quake's epicenter, was seen waylaid against the side of a house. There were no reports on the whereabouts of passengers.

With roads pretzeled and fuel in high demand along the undamaged routes heading north, the government will depend on ships and aircraft for the rescue work. Japan is sending 195 aircraft and 25 vessels to the disaster area, according to Kyodo news. U.S. fleets will join for search-and-rescue missions.

Japanese power companies warned of severe outages in the upcoming days, with energy sources in diminished supply.

On Saturday Japan's northeastern coastline, viewed from above, had the look of a dark scar. The fiercest tsunami had sent a wall of water upwards of 20 feet toward the shoreline, and the wave spread some six miles inland. At 6 a.m. local time, Prime Minister Naoto Kan surveyed the area by helicopter. Those on ground level told of screams from trapped survivors, houses turned to splinters and overtaxed hospitals and shelters.

In the Miyagino ward of Sendai city -- the hardest-hit population center -- officials set up 31 evacuation sites. They filled up with 23,000 people. This was near the area where, one day earlier, several hundred bodies had been found on the beach.

"Supplies are coming in a bit by bit, but we still don't have enough," said Hideya Yusa, in the Miyago ward office. "Initially we needed more blankets, which we still don't have enough of. So far we have distributed dried crackers, water and rice, but it wasn't enough to go around for everyone."

Some areas, such as Ootsuchi town and Sumita town in Iwate prefecture, sustained such serious damage that nobody has yet been able to get in touch with town officials. In Rikuzen Takata city, one of the worst-hit areas, some 5,000 of the town's 8,000 homes were destroyed.

Amid earlier concerns of a nuclear meltdown at one of the Fukushima plants, operated by the Tokyo Electric Power Co., some 40,000 residents were urged to evacuate -- just one of many forced migrations across the coast. Tamura city, in Fukushima Prefecture, was asked to receive residents from Okuma town, near the nuclear power plant.

"People are calm," Tamura official Densaku Nemoto said. "But we are sending public health nurses to evacuation centers to take care of the mental aspects of the evacuees. For now, volunteers are bringing in blankets and food. And we are asking the prefecture to further provide us with more food and blankets."

www.washingtonpost.com/wp-dyn/content/article/2011/03/12/AR2011031201452_pf.html