An earthquake measuring 5.5 on the Richter scale jolted 285km SW of Vaini, Tonga at 16:23:29 Hong Kong Time (08:23:29 GMT) on Wednesday, the U.S. Geological Survey said. The epicenter, with a depth of 155.4 km, was initially determined to be at 23.0061 degrees south latitude and 177.1767 degrees west longitude.