Reporting from Tokyo and Los Angeles—Japan's most punishing earthquake on record and the devastating tsunami it triggered plunged the heart of the densely populated island nation into an apocalyptic scene of blazing buildings, cratered highways, waterborne rubble and frenzied efforts to avert radiation leaks at damaged nuclear power plants.
Japan Broadcasting Corp. said more than 1,000 people had died, mostly in the northeastern part of the country.
Photos: Scenes from the earthquake
More than 100 aftershocks have jolted Japan since Friday's 2:46 p.m. temblor, including at least a dozen of magnitude 6 or higher, said Dave Applegate, a senior advisor at the U.S. Geological Survey.
The earthquake, centered just off the northeastern coastal city of Sendai, was the most powerful since a December 2004 quake and ensuing tsunami killed 230,000 people in Indian Ocean nations.
The havoc unleashed on Japan just ahead of Friday rush hour has left the nation mired in fear, suffering and hardship. Millions of people are without power, utility officials said, and they warned that outages would continue through the weekend, with rolling blackouts persisting for weeks.
Videos of the earthquake
Four trains carrying passengers along the coast at the time of the quake remain unaccounted for, East Japan Railway Co. reported. Only half of the hundreds of people reported trapped in elevators were rescued overnight, according to the Ministry of Land, Infrastructure, Transport and Tourism.
Key rail lines remained idle for a second day because of damaged track, tunnels and bridges. Service on Tokyo's vaunted subway system, the world's busiest with 8 million passengers per day, was sharply reduced pending safety inspections.
Limited air traffic resumed at major airports, including Tokyo's Narita International, but most were thronged by travelers marooned after major airlines suspended flights.
Steven Nia, a Los Angeles businessman heading for a flight home at the airport, said he slept the night in the terminal.
"I'm from California, so I recognize what an earthquake is, but I've never seen anything like this," Nia said.
Tokyo Bay, one of the busiest harbors in the world, was eerily quiet Saturday afternoon. Ships, barges and fishing boats sat idle in the still waters. The freeway across the bay was empty.
At Tokyo's railway station, hordes of people were making their way home after spending the night stranded in the capital.
Kenji Higuchi, 43, manager at the radio communications provider Japan Enix Co., said he spent the night monitoring and inspecting wireless base stations across Tokyo and slept in his office. He had to jostle for 10 minutes with throngs trying to board suburban trains just to get on the platform, he said.
"The images of destruction and flooding coming out of Japan are simply heartbreaking," President Obama told a news conference at the White House. He said the U.S. aircraft carrier Ronald Reagan was heading toward Japan to join the U.S. 7th Fleet's command ship, Blue Ridge, in the massive global relief effort.
Obama said he had spoken with Japanese Prime Minister Naoto Kan to extend condolences and "offered our Japanese friends whatever assistance is needed."
At least 45 countries scrambled disaster-relief teams, including 68 search-and-rescue units that were awaiting the Japanese government's direction on where to deploy, said Elisabeth Byrs of the U.N. Office for the Coordination of Humanitarian Affairs. A team of disaster responders sent to New Zealand by Tokyo after the Christchurch earthquake last month rushed back to help their devastated homeland.