Widespread destruction from Japan earthquake, tsunamis

• NEW: Official death tolls vary
• Radiation levels more than 8 times normal measured near nuclear plant
• Official death toll is at 184 but is expected to climb
• A 6.2-magnitude earthquake is recorded on western Honshu island

Editor's Note: Read live blogging of the Japan tsunami and earthquake. Are you there? Send your video, pictures to iReport. For more news visit CNN affiliates KHON and KHNL.

Tokyo (CNN) -- The morning after Japan was struck by the most powerful earthquake to hit the island nation in recorded history and the tsunami it unleashed -- and even as the earth continued to twitch with aftershocks -- the disaster's massive impact was only beginning to be revealed.

Hundreds of people died in the 8.9-magnitude temblor, which was centered near the east coast of Japan. The massive movement caused the formation of 30-foot walls of water that swept across rice fields, engulfed entire towns, dragged houses onto highways, and tossed cars and boats like toys. Some waves reached six miles (10 kilometers) inland in Miyagi Prefecture on Japan's east coast.

Buildings collapsed by the score, and numerous fires were ignited.

Hundreds of people were missing, Japanese media reported, citing local and national police. Tens of thousands of people were displaced, according to Japan's Kyodo News Agency.

Prime Minister Naoto Kan said the "enormously powerful" earthquake had caused "tremendous damage over a wide area."

The quake, which struck at 2:46 p.m. (12:46 a.m. ET), prompted the U.S. National Weather Service to issue tsunami warnings for at least 50 countries and territories.

The epicenter of the main quake Friday was off Miyagi Prefecture, about 230 miles (370 kilometers) northeast of Tokyo, the U.S. Geological Survey said.

Japanese broadcasters showed video of collapsed buildings and reported widespread power outages and transportation disruptions. In Tokyo, rail service was suspended, elevated highways were shut early Saturday and surface streets remained jammed as commuters tried to get to their homes in outlying areas.

Video aired by Japanese broadcaster NHK showed extensive fires in Miyagi and widespread fires in the port city of Hakodate, in the southern part of Hokkaido island in northern Japan. An oil refinery was burning in Chiba Prefecture near Tokyo, according to NHK, and firefighters could not get close enough to fight it because of the heat. And Kyodo News said fires could be seen in extensive areas of Kesennuma in Miyagi Prefecture.

Also in Miyagi, officials reported that a train had derailed and authorities had lost contact with four trains in coastal areas, Kyodo reported, citing the East Japan Railway Company.

And a dam in Fukushima Prefecture failed, washing away homes, Kyodo reported. There was no immediate word of casualties, but the Defense Ministry said 1,800 homes were destroyed.

The National Weather Service sent a warning to 50 countries and territories it said could be affected by the tsunami.

Scores of aftershocks jarred the country Saturday, punctuated by a pair of strong earthquakes in the early morning, including one with a magnitude of 7.1 and another with a magnitude of 6.6.

Japan's trade minister, Banri Kaieda, said a small radiation leak could occur at the Fukushima nuclear plant, Kyodo reported Saturday.

Citing the Nuclear and Industrial Safety Agency, Kyodo reported Saturday morning that radiation levels more than eight times normal were being measured at a monitoring post near the plant's main gate.

Prime Minister Kan told reporters he would board a helicopter to inspect the plant and the rest of the affected region from a helicopter.

The government had ordered the evacuation of residents nearest the plant as efforts to keep it cool after it was shut were initially hampered.

The confirmed death toll stood at 133, not counting the 200 to 300 bodies -- apparently drowned -- found in Sendai, Miyagi Prefecture, Kyodo said, citing police.

But NHK, also citing police, said at least 388 people were confirmed dead and more than 700 were missing across several prefectures.

Kyodo predicted the death toll would surpass 1,000.

The news agency, citing Japan's defense forces, also said 60,000 to 70,000 people were being evacuated to shelters in the Sendai area of Miyagi Prefecture.

The prime minister said an emergency task force had been activated, and he appealed for calm. The government dispatched 8,000 troops to assist in the recovery effort and asked for U.S. military assistance, according to Kyodo.

A spokesman for the U.S. military bases in Japan said all service members were accounted for and there were no reports of damage to installations or ships.

U.S. President Barack Obama offered his condolences and said the United States was standing by to help "in this time of great trial."

The U.S. Navy initiated reconnaissance flights to map the disaster zone and was moving the aircraft carrier USS Ronald Reagan into position to assist the Japanese government with relief efforts, defense officials said.

Two search-and-rescue teams, totaling more than 140 people, were en route, the U.S. Agency for International Development said.

Images from Japanese media and CNN iReporters showed smoke pouring from buildings and water rushing across fields, carrying away entire structures.

"I wasn't scared when it started ... but it just kept going and going," said Michelle Roberts, who lives in central Tokyo. "I won't lie, it was quite scary. But we are all OK. We live on the third floor, so most everything shook and shifted."

The quake toppled cars off bridges and into waters underneath. Waves of debris flowed like lava across farmland, pushing boats, houses and trailers. About 4 million homes had no power in Tokyo and surrounding areas.

• Earthquakes
• U.S. Geological Survey

The quake also disrupted rail service and affected air travel. Hundreds of flights were canceled, Kyodo said. Some 13,000 people were stranded at the Narita airport, and 10,000 were stuck at the Haneda airport, the news agency said.

At Tokyo Station, one of Japan's busiest subway terminals, shaken commuters grabbed one another to stay steady as the ground shook. Dazed residents poured into the streets, and offices and schools were closed. Children cried.

Residents said that although earthquakes are common in Japan, Friday's stunned most people.

"This was larger than anyone expected and went on longer than anyone expected," said Matt Alt, who lives in Tokyo.

"My wife was the calm one. ... She told us to get down and put your back on something, and leave the windows and doors open in case a building shifts so you don't get trapped."

Richard Lloyd Parry said he looked through a window and saw buildings shaking from side to side.

"Central Tokyo is fine from what we see, people are calm ... and not going inside buildings," he said.

Such a large earthquake at such a shallow depth -- 15.2 miles (24.5 kilometers) -- creates a lot of energy, said Shenza Chen of the U.S. Geological Survey.

The impact was felt far and wide. In McKinleyville, California, a wave swept three men into the Pacific Ocean as they were reportedly trying to take photos of the incoming tsunami waves, according to the U.S. Coast Guard.

Two of the men returned to shore, but one remained unaccounted for, said the Coast Guard, which was using helicopters to search for him.

Japanese government officials said large tsunami waves were still a risk to coastal Japan, and they urged residents in coastal areas to move to higher ground.

The tsunami brought waves of nearly 7 feet to a harbor in Maui, authorities said, but other areas reported lower levels.

On the U.S. mainland, wave heights from Alaska to California ranged from under a foot to over 8 feet. The highest measurement, 8.1 feet, was at Crescent City, California.

Tsunamis are a series of long ocean waves that can last five to 15 minutes and cause extensive flooding in coastal areas. A succession of waves can hit -- often the highest not being the first, CNN meteorologist Ivan Cabrera said.

Humanitarian agencies were working with rescue crews to reach people affected by the earthquake and tsunami.

"When such an earthquake impacts a developed country like Japan, our concern also turns to countries like the Philippines and Indonesia, which might not have the same resources," said Rachel Wolff, a spokeswoman for World Vision.

Wolff said her agency is helping people in Japan and teaming up to help others in countries along the path of the tsunami.

The quake was the latest in a series around Japan this week.

On Wednesday, a 7.2-magnitude earthquake struck off the coast of Honshu, the country's meteorological agency said. Early Thursday, an earthquake with a preliminary magnitude of 6.3 struck off the same coast.

Friday's quake is the strongest earthquake in recorded history to hit Japan, according to U.S. Geologic Survey records. The previous record was an 8.6-magnitude earthquake that struck near the Chubu Region near southwestern Honshu on October 28, 1707, that may have killed 5,000 people, CNN meteorologist Sean Morris said.

That quake generated a 33-foot (10-meter) tsunami wave, and some scientists believe the quake may have triggered the eruption of Mount Fuji 49 days later, Morris said.

The world's largest recorded quake took place in Chile on May 22, 1960, with a magnitude of 9.5, the USGS said.

CNN's Kyung Lah, Faith Karimi, Ed Payne, Catherine E. Shoichet, Kevin Voigt and Sean Morris contributed to this report.