By Tetsushi Kajimoto and Izumi Nakagawa
TOKYO (Reuters) - Japanese manufacturers' morale rose for a fifth straight month in January to a 2-1/2 year high and the service sector's mood jumped to its highest levels since mid-2015, a Reuters poll showed, thanks to a weak yen and buoyant share prices.
The latest Reuters Tankan underscores growth prospects for the world's third largest economy, but uncertainty lies ahead after U.S. President-elect Donald Trump is inaugurated on Friday, with his protectionist agenda casting doubts over the smooth conduct of global trade.
The Reuters' monthly poll - which tracks the Bank of Japan's key quarterly tankan - found confidence at manufacturers and service-sector firms slipping over the next three months.
In the poll of 531 large- and mid-sized firms, conducted between Jan. 4 and 17 and in which 266 responded, the sentiment index for manufacturers rose to 18 from 16 in December, driven by industries such as electronics and machinery.
It was the highest reading since August 2014, but is expected to fall back to 16 in April.
"I felt manufacturers were becoming positive about capital spending from last August or September. The yen weakening following the U.S. election spurred an upswing in the economy," a manager at a electric machinery firm wrote in the survey, which companies answer anonymously.
However, some companies also expressed cautious views about the future, and others complained about weak demand at home as well as in China and emerging market economies.
"The global economy's trend is unclear. Currencies and oil prices are fluctuating violently," a chemicals company said.
The service-sector index rose to 30 from 19 in December, boosted by retailers and wholesalers, somewhat easing concerns about the private consumption that constitutes about 60 percent of the economy.
It was the highest reading since June 2015, but it is seen slipping to 28 in April.
The BOJ's December tankan showed the mood among big Japanese manufacturers improved for the first time in six quarters to hit a one-year high, as the weakening yen and a pick-up in the global economy brightened prospects for exporters.
Japan's central bank last month held off on expanding stimulus, underscoring a market view that it will stand pat unless a severe external shock threatens to derail economic recovery.
It holds its next rate review at the end of this month.
The Reuters Tankan indexes are calculated by subtracting the percentage of pessimistic respondents from optimistic ones. A negative figure means pessimists outnumber optimists.