"We are all ok. Lots of messes, think fish tanks and china cabinets," Carrie Elizabeth Barnes Broman told friends in a message. "MeySen is housing staff and students' families in the school. ... No electricity or gas obviously - water available depending on building."
Randy Castle, an American man working in Japan, said his hotel lobby was full of people overnight who couldn't make it home from work.
"It started and it lasted a good five minutes, lots of shaking and very scary. I'm on the 11th floor, just down the street from the Tokyo tower," Castle said.
The Tokyo tower, a famed landmark in Japan, is now bent.
"It was a lot of swaying, you could hear the building creaking in it ... you could see the shades shaking back and forth," Castle said. "The people that I work with here in Tokyo, it was normal for them, but shortly after that it started to get scary the longer it went."
"We were just hanging out in Shibuya [Tokyo] today and walking down the street and all of a sudden felt like we were on a boat and looked up and tall buildings were going crazy, looking like they were going to tip over," said Kevin Williams, an American vacationing in Tokyo.
It's the strongest earthquake the world has seen since the 9.1 magnitude Indian Ocean quake in 2004, which triggered a massive tsunami. The combination of the quake and tsunami left 230,000 people dead.
The Japan quake hit at 2:46 p.m. local time in Japan, and lasted an astonishing five minutes. To put that in perspective, the devastating earthquake in Northridge, Calif., in 1994 lasted just six seconds.
"The bigger the earthquake, the larger the size of the fault that has to rupture to make it happen…you're seeing waves generated along a huge fault," Dr. Kate Hutton, a seismologist at the California Institute of Technology, said.
At least 80 aftershocks above magnitude 5.0 -- and some as large as 7.4 -- have struck Japan, reversing the path of rivers, washing away boats and cars, and leaving buildings shaking like jelly.
There are reports of a missing train full of dozens of commuters in the earthquake region and a boat ripped from the docks of Miyagi with 80 workers on board being swept out to sea in the tsunami.
"We have to watch for chemical explosions, gas leaks, fires ... the agony is just beginning," Dr. Michio Kaku, a physicist, said. "Earthquakes take place in stages. ... We are only in act one. We have yet to go to act two."
A "nuclear emergency" was declared at the Fukushima Daiichi power plant after a power outage disabled the cooling system at one reactor and pressure built up. Nearly 3,000 people were evacuated from the region surrounding the plant.
Later, the company in charge of the plant and another plant nearby reported four more reactors had cooling system failures, the Associated Press reported.
Kaku, a physicist who also has family in Japan, said that the tsunami struck in the pivotal "Ring of Fire," an arc of earthquake and volcanic zones stretching around the Pacific. The region is where 90 percent of the world's earthquakes occur.
ABC Radio and the Associated Press contributed to this report.