The Japan Meteorological Agency said Thursday night's earthquake was the strongest to strike parts of Tokyo and Saitama since the mega-quake shook the country's northeast in March 2011.
Thursday's quake had a preliminary magnitude of 6.1. It jolted parts of Tokyo and Saitama with an intensity of five-plus on the Japanese scale of zero to seven.
The 2011 quake had a magnitude 9.0. It registered an intensity of six-minus in a town in Saitama Prefecture and five-plus in other parts of Saitama and large areas of Tokyo, including its 23 wards.