A 10cm-high wave has hit the shore in northeastern Japan this morning after a magnitude 6.8 quake prompted a tsunami warning.

The tremor struck at 8.06 am in the Pacific, some 210km east of Miyako at a depth of 10km.

There were no immediate reports of injuries or casualties following the quake and minor tsunami, local media said.

It was earlier reported that the quake was a magnitude 6.9 but this was later revised.

Local authorities in Iwate issued evacuation advisories to more than 19,000 people after the quake, Japan's public broadcaster NHK said.

There was no damage to any of nuclear reactors in the region as they have been off-line since 2011, NHK said.