Tokyo, Aug 11 (Xinhua) An undersea earthquake measuring 6.6 on the Richter scale Tuesday jolted eastern Japan, 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 report of casualties or damage, it said.

The operation of two nuclear reactors at Hamaoka plant in Omaezaki in Shizuoka prefecture was immediately suspended.

The Central Japan Railway Co. has also suspended the operation of its Shinkansen bullet trains following the quake.