The most recent nuclear test took place at 0054 hours GMT on 25 May 2009 in the Democratic People's Republic of Korea (DPRK) or, more usually, North Korea. According to the US Geological Survey the underground explosion had a magnitude of 4.7 on the Richter scale with a centre about 70 km (43 miles) northwest of Kimchaek and close to the site of the North Korean nuclear test that took place in 2006. Russian experts believe the yield to have been between 10 and 20 kilotons - as powerful as the bombs the USA used against Japan in World War II and many more times as powerful as that in the 2006 test. According to media reports, the force of the explosion made the ground shake in the Chinese border city of Yanji, 209 km (130 miles) away.