TOKYO - A strong earthquake with a preliminary magnitude of 6.1 jolted the Tokyo region on Monday morning, but no tsunami warning was issued and there were no immediate reports of serious damage.
Two runways at Narita International Airport near Tokyo were closed for checks but soon reopened, public broadcasterNHK said.
Some high speed bullet train lines experienced minor delays because power stopped briefly, and some local lines were halted.
Officials warned of possible aftershocks and landslides.
A nuclear reactor in Tokaimura, about 68 miles northeast of Tokyo, was operating normally, NHK said.
The focus of the quake, which struck at 7.22 am (10.22am NZT), was about 37 mile below the earth's surface in Chiba prefecture, east of Tokyo, the Japan Meteorological Agency said.
"There have been no reports of damage," Masao Ikeda, a local official in the town of Kamisu told NHK.
"I was at home at the time of the earthquake. It was a big earthquake with sharp shaking from side-to-side," Ikeda said.
Earthquakes are common in Japan, one of the world's most seismically active areas, and the country accounts for about 20 percent of the world's earthquakes of magnitude 6 or greater.
In October 2004, an earthquake with a magnitude of 6.8 struck the Niigata region in northern Japan, killing about 40 people and injuring more than 3,000.
That was the deadliest quake since a magnitude 7.3 tremor hit the city of Kobe in 1995, killing more than 6,400.
