The Nikkei stock index surged Thursday to its highest close in about six years as sentiment brightened on buoyant US and European shares and the yen’s further depreciation against other major currencies. According to (Kyodo) news agency, the 225-issue Nikkei Stock Average gained 277.49 points, or 1.8%, from Wednesday to 15,727.12, its highest close since Dec. 12, 2007. The broader Topix index of all First Section issues on the Tokyo Stock Exchange rose 13.96 points, or 1.12%, to 1,261.04. Most of the 33 sectors advanced, with marine transport, paper and pulp, and consumer financing sectors leading the gains. Mining, oil and coal sectors were the only declining sectors.