The Japan Meteorological agency reports a 7.4 quake in Miyagi prefecture, northeastern Japan, which hit at 11:32pm local time. USGS reports the same, about 60 miles (96km) from Sendai, Japan, and about 25 miles (40km) below the sea-bed. Tsunami warnings, the first since the catastrophic March 11 quake and tsunami, are being issued throughout the region. This quake is considered to be an aftershock of the March 11 seismic event.
NHK TV is reporting that the nuclear safety agency says the nuclear power plants in the region have been shut down, but that workers at Fukushima Daiichi are being (or have been) evacuated just now. TEPCO, the operator of the stricken nuclear plant, tweeted just now that they are evaluating whether this quake has caused any further damage but that there are no reports of injuries and no new information suggesting new damage.
The area where this quake struck is the same region most affected by the March 11 disaster, so the earth there is generally unstable, and populations in the area are already vulnerable.
Police report that the number of people confirmed dead in the March 11 earthquake and tsunami is now 12,608, with an additional 15,073 listed as missing.
Update: No reports of tsunami damage, sounds like the wave weakened before hitting land. The tsunami warning has been lifted.
Update: At Tohoku Electric's Onagawa nuclear power plant, in Miyagi, 2 of the three external power grids have lost power. The three reactors at this site have been in cold shutdown since March 11. No change has been observed in radiation levels today.
Update: NISA (Japan nuclear safety agency) press conference, live notes: several nuclear power plants in the area have lost power, and are now relying on emergency diesel power sources.
Notes from a live TEPCO press conference taking place now. A representative is on NHK TV saying:
"Once the tsunami warning has been lifted, we will go to reactors 3 and 4 to check, but we have not heard of any situation at the reactors or the vertical tunnels. At Fukushima Daini we have looked into any issues with the facilities and personnel and have verified everything is alright. Power is not interrupted."
"For Fukushima Daiichi: no reported injuries. There were two workers near reactors 1 and 2, and there were 7 workers near the intake site who have not been injured; all have all taken shelter in our seismic-resistant building. we are continuing the injection operation at reactors 1, 2, and 3; water injection is continuing. As for reactor No. 1 where nitrogen has been injected, we have seen no changes. The central control room is located remotely. Reactors 1, 2, 3: water levels have remained the same. Reactors 5, 6, no anomalies. Reactors 3 and 4, every 6 hours we visit the central control rooms. the next scheduled visit was for 2400 hours. As soon as safety is verified and the tsunami warning is lifted we will visit the control rooms for reactors 3 and 4."
Update: NHK is reporting at least one fire in Yamagata city, widespread blackout in Yamagata; traffic lights not working in Sendai.
Update: Here's a handy map showing where nuclear power plants are located in Japan. (Source: METI, via Daniel Garcia, via Antonio Delgado).