SHANGHAI, April 2 (Reuters) - China's Tiangong-1 space station re-entered the earth's atmosphere and burnt up over the South Pacific on Monday, the Chinese space authority said. The "vast majority" of the craft burnt up on re-entry, at around 8:15 a.m. (0015 GMT), the authority said in a brief statement on its website, without saying exactly where any pieces might have landed. Brad Tucker, an astrophysicist at Australian National University, said the remnants of Tiangong-1 appeared to have landed about 100 km (62 miles) northwest of Tahiti. "Small bits definitely will have made it to the surface," he told Reuters, adding that while about 90 percent would have burnt up in the atmosphere and just 10 percent made it to the ground, that fraction still amounted to 700 kg (1,543 lb) to 800 kg (1,764 lb).