* Nikkei extends morning's gains, up 1.4 pct, Topix up 1.7 pct * Weak yen lifting exporters By Ayai Tomisawa TOKYO, July 30 (Reuters) - Japan's Nikkei average rose Tuesday afternoon, led by exporters as the yen weakened against the dollar, while sentiment was boosted after Chinese shares rose for the first time in five days. The benchmark Nikkei gained 1.4 percent to 13,848.50 in early afternoon trade. It was up only 0.4 percent at the midday break. The market was sensitive to currency levels after the dollar touched a nearly one-month low of 97.61 yen on Monday, but futures buying kicked in after the lunch break as the dollar rose against the yen, analysts said. The dollar last traded at 98.35 yen. "As the dollar is comfortably trading above 98 yen, those who were taking profits lately decided to buy back," said Isao Kubo, equity strategist at Nissay Asset Management. Exporters were strong, with Toyota Motor Corp rising 3.2 percent, Sony Corp 3.6 percent and Panasonic Corp 1.7 percent. A weak yen boosts exporters' competitiveness abroad as well as their earnings when repatriated. The broader Topix gained 1.7 percent to 1,147.30. The Shanghai Composite Index, which had losses the past four days, was up 1.1 percent. The gain is "helping the mood as weakness in Chinese shares has been a factor dragging down the Japanese market," Nissay's Kubo said.