* Tsunami advisory lifted an hour after quake
* Nuclear watchdog, Tepco: no impact on nuclear power plants
* Same area was struck by March 11 quake, tsunami (Updates with tsunami advisory lifted, no impact on nuclear plants)
TOKYO, June 23 (Reuters) - An earthquake with a preliminary magnitude of 6.7 struck off the coast of Iwate prefecture in northeast Japan on Thursday, one of the areas devastated by the March 11 quake and tsunami, but there were no immediate reports of damage or injuries.
A warning of a tsunami of up to 50 cm (20 inches) was lifted about an hour after the quake, which occurred around 6:51 a.m. (2151 GMT Wednesday), but authorities warned residents to be wary of mudslides.
Tokyo Electric Power Co , struggling to control radiation leaks at its Fukushima Daiichi nuclear plant due to damage in the March disaster, said there was no impact from Thursday's quake on its efforts to bring the reactors under control.
The Nuclear and Industrial Safety Agency said there were no reports of abnormalities at Tohoku Electric Power's Higashidori and Onagawa nuclear power plants in northeast Japan. Operations of these reactors have been halted since the March disaster.
The focus of the tremor was 20 km (12 miles) below the seabed off Iwate and about 500 km (300 miles) northeast of Tokyo, the Japan Meteorological Agency said. (Reporting by Edwina Gibbs and Yoko Kubota)