The quake, the largest to hit Japan since record-keeping began in the late 1800s and one of the biggest ever recorded in the world, struck at 2:46 p.m. about 80 miles off the eastern coast.
Officials have confirmed about 1,800 deaths, including 200 people whose bodies were found Sunday along the coast, but police in one of the worst-hit areas estimated the toll there alone could eventually top 10,000. More than 1,700 were missing and 1,900 were injured.
However, the true extent of the disaster was not known because roads to the worst-hit areas were washed away or blocked by debris and airports were closed.
- Nuclear officials confirmed a hydrogen explosion occurred at Unit 3 of Fukushima Dai-ichi plant Monday morning. The inner reactor container remained intact and there was little possibility that radioactive material had been spewed into the air, an official said. Three people were injured and seven were missing after the explosion. More than 180,000 people have evacuated the area, and up to 160 may have been exposed to radiation.
- Soldiers and officials in northeastern Japan warned residents that the area could be hit by another tsunami and ordered residents to higher ground. But despite reports of a new tsunami threat, a government spokesman said there was no oncoming tsunami detected.
- The USS Ronald Reagan and other U.S. ships in the waters off the quake zone have been repositioned away from the Fukushima power plant after three helicopters traveled through a low-level radioactive plume that originated from the plant. When the crews returned to the carrier, they were washed down with soap and water and no further contamination was detected. As a precautionary measure, the Reagan and other ships have moved out of the downwind direction of the site.
- Japan's top government spokesman, Chief Cabinet Secretary Yukio Edano, said Tokyo Electric Power has held off on imposing rolling blackouts, but is calling for all to try to limit electricity use.
- Nuclear plant operators were frantically trying to keep temperatures down in a series of nuclear reactors - including one where officials feared a partial meltdown could be happening Sunday - to prevent the disaster from growing worse at the nuclear power plant in Fukushima, located 170 miles north of Tokyo. Japan has a total of 55 reactors spread across 17 complexes nationwide.
- A complete meltdown - the collapse of a power plant's ability to keep temperatures under control - could release uranium and dangerous contaminants into the environment and pose major, widespread health risks.
- Japanese officials raised their estimate Sunday 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. Japan's prime minister called the crisis the most severe challenge the nation has faced since World War II.
- Dozens of countries have offered assistance. Two U.S. aircraft carrier groups were off Japan's coast and ready to provide assistance. Helicopters were flying from one of the carriers, the USS Ronald Reagan, delivering food and water in Miyagi. Two other U.S. rescue teams of 72 personnel each and rescue dogs arrived Sunday, as did a five-dog team from Singapore.
- The Japanese government doubled the number of soldiers deployed in the aid effort to 100,000 and sent 120,000 blankets, 120,000 bottles of water and 29,000 gallons (110,000 liters) of gasoline plus food to affected areas. However, Prime Minister Naoto Kan said electricity would take days to restore and it would be rationed with rolling blackouts to several cities, including Tokyo.
- The United States and 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.
- Rikuzentakata, a port city of over 20,000, was virtually wiped out by the tsunami. To the south, in Miyagi prefecture, the police chief estimated the casualty count at more than 10,000. Miyagi has a population of 2.3 million and is one of the three prefectures hardest hit in Friday's disaster. Fewer than 400 people have officially been confirmed as dead in Miyagi.
- At a large refinery on the outskirts of the hard-hit port city of Sendai, 100-foot (30-meter) -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.
Scientists at Caltech provided an update on the earthquake on Sunday, warning Japan to brace for even more major aftershocks.
Dr. Lucy Jones of the U.S. Geological Survey said 200 earthquakes of magnitude 5 or larger were recorded within the sequence, with 20 of them being foreshocks that occurred in the two days before the main shock on Friday.
Jones said on average, the largest aftershock in a sequence is 1.2 units of magnitude smaller than the main shock, which will mean a 7.7-magnitude aftershock in Japan's case.
"We've had one 7.1. We've had about 30 magnitude-6s. No one would be surprised if there's a magnitude-7 aftershock within this sequence," Jones said.
President Barack Obama has voiced condolences for the people who perished in the earthquake, saying the United States "stands ready to help" in any way it can.
"The friendship and alliance between our two nations is unshakeable, and only strengthens our resolve to stand with the people of Japan as they overcome this tragedy," Obama said in a statement.
Dozens of cities and villages along a 1,300-mile stretch of coastline were shaken by violent tremors that reached as far away as Tokyo. In Tokyo, buildings shook, and debris rained down on the streets below.
"It was a lot of swaying. You could hear the building creaking. As it was going, we were told to get down, and we could see the shaking back and forth," said one quake survivor.
Witnesses said the shaking lasted close to five minutes. There have been dozens of aftershocks too, including a 7.4-magnitude one about 30 minutes later. At least 19 aftershocks were felt, most of them more than magnitude 6.0.
Tokyo has held up well so far, with no reports of serious damage. Building codes in Japan are some of the most stringent in the world. However, farther north along the coast, the devastation is widespread. After the quake, a series of tsunamis hit low-lying coastal villages and towns. Some of the tsunamis reached a height of 23 feet.
The walls of water swallowed anything in their path, including buildings, cars and people. Boats were tossed about like toys and some ended up being pushed very far inland.
There are reports of hundreds of bodies washing up on shore, and there are thousands of people missing.
The ceiling in Kudan Kaikan, a large hall in Tokyo, collapsed, injuring an unknown number of people, NHK reported. In central Tokyo, trains were stopped and passengers walked along the tracks to platforms.
ABC7 has partnered with the Red Cross to raise money for the victims of the devastating Japan earthquake and tsunami.
Donations by check can be sent to:
ABC7 Japan Disaster Relief Fund
P.O. Box 5967
Glendale, CA 91221
All checks should be made out to the Red Cross, with "Japan Earthquake and Tsunami Relief" in the memo line.
The Associated Press and City News Service contributed to this report.