Tokyo, Aug 11 (Xinhua) An undersea earthquake measuring 6.6 on the Richter scale jolted eastern Japan early Tuesday, prompting officials to issue a tsunami warning, the meteorological agency said.

The quake occurred at 05.07 a.m., and its epicentre was located some 20 km under the sea in Suruga Bay, said the agency. There was no immediate report of casualties or damage, it said.