* Exporters lead gainers as yen nears 100-mark to dollar * All of the 33 sectors on Topix rise * Mitsui Eng jumps 13.6 pct on report of merger talks Kawasaki Heavy By Tomo Uetake TOKYO, April 22 (Reuters) - The Nikkei share average climbed 1.9 percent to a near five-year high on Monday morning, with exporters surging as the yen weakened after the Group of 20 leading economies stopped short of criticising Japan's sweeping monetary expansionary policies. At the midday break, the Nikkei was up 258.23 points at 13,574.71 after trading as high as 13,611.58, its highest level since June 2008. It briefly broke above the 13,608.19 mark, a settlement price of options contracts, known as "options SQ", expiring this month on April 12. "Although the yen hasn't seen 100 against the dollar yet, the market's expectation for further depreciation is high, and thus the stocks are performing so well," said Hiroyuki Fukunaga, the chief executive of Investrust. Major exporters charged higher as the dollar firmed against the yen to within a whisker of 100 after the G20 refrained from singling out Tokyo's reflationary policies as some in the markets had feared. The yen last traded at 99.79 to the dollar. A weaker yen inflates exporters' overseas earnings when repatriated. Toyota Motor Corp rose 2.2 percent and was the third most-traded on the main board by turnover, while rival Mazda Motor Corp soared 6.3 percent. Canon Inc , TDK Corp and Olympus Corp were up between 2.4 and 5 percent. In a communique after a two-day meeting, the G20 simply said it would be "mindful" of possible side effects from extended periods of monetary stimulus. The Bank of Japan on April 4 stunned financial markets by announcing a sweeping monetary expansion programme aimed at breaking a deflationary cycle and ending two decades of stagnation, promising to inject $1.4 trillion into the world's third-largest economy in less than two years. "I worried that the G20 countries would criticise Japan's easing monetary policies," said Ryota Sakagami, chief strategist at SMBC Nikko Securities. "The market uptrend will continue ... I think sooner or later the Nikkei will reach 14,000. For the moment, the one concern is still the weak global economy, especially the weak U.S. macro economic indicators." Sakagami said domestic-focused companies were likely to outperform exporters in the next few months, although the yen's weakness has lifted the appeal of export-driven firms on Monday. The broader Topix index advanced 1.9 percent to 1,148.52 by the midday break, with volume at 71 percent of its full daily average for the past 90 trading days. All of the 33 sectors on the Topix posted gains. MITSUI ENGINEERING JUMPS Mitsui Engineering & Shipbuilding Co Ltd jumped 13.6 percent to a near two-year high after the Nikkei newspaper said Mitsui and Kawasaki Heavy Industries Ltd were set to begin merger talks. Shares of Kawasaki Heavy edged up 1.8 percent. Financials, which are expected to benefit from the reflationary drive, were also in demand, with Nomura Holdings , Japan's top brokerage, up 3 percent and Mitsubishi UFJ Financial Group adding 2.5 percent. The benchmark Nikkei has rallied 57 percent and the yen has weakened 23 percent against the dollar since mid-November, when Shinzo Abe, who became Prime Minister in December, promised bold monetary and fiscal expansionary policies during his election campaign. In terms of valuations, Japanese equities carry a 12-month forward price-to-earnings ratio of 14.7, a level not seen since June 2010 but still below its 10-year average of 16.4, according to Thomson Reuters Datastream.