At 2:46 p.m, Tokyo time, an 8.9 magnitude earthquake off the northeast coast of Japan sent a powerful wall of water inland, destroying coastal towns and property.
Waves as tall as 33 feet struck the city of Sendai in the Miyagi Prefecture, and the BBC is reporting that 88,000 people are missing and 200-300 are confirmed dead (Google has set up an online person-finder service). The earthquake, which was the largest to ever hit Japan and the seventh largest in recorded history, occurred underwater 81 miles east of Sendai and caused strong quakes in surrounding prefectures and cooling and mechanical failures in two nuclear plants (UPDATE: some mechanical problems are under control, but pressure is rising in one of the reactors).
Aftershocks are being reported as I'm typing this, and coastal areas on both sides of the Pacific are evacuating in fear of further tsunamis (so far the Philippines and Hawaii have been spared any large waves). Here's the link to the Red Cross' relief efforts, and here's footage of the tsunami and quake damage both from on-location video and various news agencies:
You can see more eyewitness videos on Citizentube.