The massive quake was felt strongest in Miyagi Prefecture, where it came in at 7, the maximum reading on the Japanese seismic intensity scale, the Meteorological Agency said.
Police said at least 32 people died across an extensive area of eastern Japan ranging from Iwate and Miyagi prefectures in the northeast to Tokyo. The 2:46 p.m. quake also set off fires at scores of locations, as well as a huge refinery inferno in Chiba Prefecture.
The quake was felt hundreds of kilometers away, including in Tokyo, where buildings swayed for a long time and people swarmed out of them.
The temblor is the strongest ever to hit the quake-prone archipelago, the Meteorological Agency said, with a magnitude surpassing the 7.9 registered in the 1923 Great Kanto Earthquake in Tokyo and its vicinity, which left more than 140,000 people dead.
The quake struck at a depth of around 10 km and originated 130 km east-southeast in the Pacific off the coast of the Ojika Peninsula in Sendai, the agency said.
The agency issued a rare warning for a huge tsunami for the Pacific coastal region from Hokkaido to Tokushima Prefecture.
The agency also called for the public to stay alert over the next month for aftershocks that could register magnitude 7 or more and trigger more tsunami.
A 10-meter tsunami was observed at Sendai port at around 3:55 p.m., police said.
A wide, muddy stream was seen moving rapidly across a residential area near the Natori River in Sendai on live TV coverage by NHK, leveling everything in its path, while other coverage showed about 20 cars being washed into the sea when a tsunami hit Kamaishi port.
At least two Japan Coast Guard patrol boats from the 2nd Coast Guard Regional Headquarters in Shiogama were washed away by the tsunami, coast guard officials said.
The runways at Sendai airport were also submerged.
Fire authorities in Miyagi's Kesennuma said a number of buildings, including houses, were seriously damaged by the quake.
A 7.3-meter-high tsunami hit Soma port in Sendai and elsewhere, the agency said, adding a 4.1-meter tsunami was observed in Kamaishi port in Iwate Prefecture.
Residential areas in several areas were flooded and scores of vehicles, boats and a storage tank were washed away by tsunami.
Fire authorities in Miyagi's Kesennuma area said a number of buildings, including houses, were seriously damaged by the quake.
According to Tohoku Electric Power Co., power outages hit Aomori, Akita and Iwate prefectures and most of Miyagi and Yamagata prefectures. Part of Fukushima and Niigata prefectures also were blacked out, the utility said.
Self-Defense Forces personnel were immediately dispatched to Miyagi Prefecture following a request from Gov. Yoshihiro Murai.
All ships docked at the Maritime Self-Defense Force's base in Yokosuka, Kanagawa Prefecture, were deployed off Miyagi, and eight fighter jets took off from four bases of the Air Self-Defense Force to check the quake damage.
There were unconfirmed reports that bridges collapsed in Saitama and Iwate prefectures, while the Ministry of Economy, Trade and Industry received no immediate reports of abnormalities at nuclear plants in the areas hit by the quake.
The quake also caused an emergency cooling system at the No. 1 reactor of the Fukushima No. 2 nuclear power plant to be activated, the industry ministry said.
Tokyo Electric Power Co. notified the ministry of the move, the ministry said, adding that monitors outside the facility have detected no abnormalities.
The Onagawa nuclear power plant in Miyagi Prefecture automatically halted operations. Its operator, Tohoku Electric Power Co., was checking whether it suffered any damage.
The quake affected key transportation systems, including Narita International Airport, which shut down its runways for safety checks. The airport instructed passengers to withdraw from the terminals.
Haneda airport in Tokyo initially closed all of its runways for safety checks, but reopened and gave priority to arriving planes.
There were no immediate reports of bullet trains derailing, which in the Tohoku region are operated by East Japan Railway Co. All shinkansen services were stopped, JR East said.
Cell phone services were halted in various parts of Japan. NTT Communications reported that long-distance telephone calls on land lines, as well as international calls, had difficult connections.
Meanwhile, in Tokyo, the Metropolitan Police Department said many people were injured when part of the Kudan Kaikan hall in Chiyoda Ward collapsed. Several fires were reported.
The metropolitan government said it shut 19 floodgates to gird for possible tsunami.
Fires were reported across wide area, including at an ironworks in Chiba Prefecture. An explosion hit a Cosmo Oil refinery in Chiba Prefecture, where one person was reported severely injured, and two others experienced minor injuries.
In Takahagi, Ibaraki Prefecture, a woman died when a roof collapsed at a massage parlor after the quake, and another fatality was reported in Haga, Tochigi Prefecture, when a factory wall collapsed.
A 67-year-old man died after being hit in the head by part of a stone wall in Chiba Prefecture, while a woman in her 50s died from injuries inflicted when part of the roof of a hall collapsed in Tokyo.
