A powerful earthquake has struck off Japan's north-eastern coast, shaking buildings in Tokyo and forcing people out of their homes, witnesses said.

Japan issued its most serious tsunami warning, saying a wave as high as 6m (20ft) could strike the coast near Miyagi prefecture.

US officials said the 8.8-magnitude quake struck about 250 miles (400km) from Tokyo at a depth of 20 miles.

TV pictures showed a wave crashing into the Pacific coast.

The surge of water carried cars and ships as it surged through a coastal town.