A strong earthquake with a preliminary magnitude of 6.1 jolted Japan's Kanto region Monday morning, but no tsunami warning was issued, the Japan Meteorological Agency said.

　　The quake occurred at 7:22 a.m. (22:22 GMT Sunday), the agencysaid. There were no immediate reports of casualties or damage.

　　Runways at Narita airport near Tokyo were briefly closed afterthe quake but no irregularities were found, the Kyodo news agency quoted airport officials as saying.

　　Railway services were suspended on part of the JR Sobu Line.