The magnitude 8.9 offshore quake was followed by at least 19 aftershocks, most of them of more than magnitude 6.0. Dozens of cities and villages along a 2,100-kilometer stretch of coastline were shaken by violent tremors that reached as far away as Tokyo, hundreds of kilometers from the epicenter.

A tsunami warning was issued for the entire Pacific, including areas as far away as South America, the entire U.S. West Coast, Canada and Alaska.

Japan’s Fire and Disaster Management Agency said at least 30 people were killed. “The earthquake has caused major damage in broad areas in northern Japan,’’ Prime Minister Naoto Kan said at a news conference.