The quake in the Fukushima Prefecture is the largest to strike Japan in 140 years and was powerful enough to shake buildings in Tokyo some 250 miles away.
At least 19 people have been killed but the death toll is expected to rise. The number of injured remains unclear.
According to reports, some of the dead were crushed by falling debris as their houses collapsed.
A 10-metre high tsunami swept through Onahama city, carrying away cars, trucks, houses and other buildings. A 10-metre wall of water was also reported in Sendai city in northeastern Miyagi prefecture.
A tsunami warning has been extended to most of the Pacific basin, with a tsunami watch issed for the entire western coast of the US and Canada.
World Vision Japan said it was assessing the scale of the damage and considering its response.
“We would like to express our sincere sympathy to the victims of this earthquake,” the organisation said in a statement.