A 7.5 magnitude quake has struck close to New Caledonia in the Pacific, with a tsunami alert issued for coasts within 1,000km (620 miles).The quake struck at a depth of about 10km at 04:18 GMT, the US Geological Survey reports.The epicentre was recorded as 168km east-south-east of Tadine, a town on one of New Caledonia's Loyalty Islands.New Caledonia is part of the Pacific's "ring of fire", where many earthquakes occur.It is a special collectivity of France with a population of about 270,000.New Zealand's ministry of civil defence and emergency management tweeted that there was no tsunami threat to the nation's coasts.The USGS also recorded a series of aftershocks, two of them at 5.9 magnitude.