GLOBAL MARKETS-Shares rally; Japan authorities rattle sabers on yen selling

(Updates as of 0934)

By Kevin Buckland, Amanda Cooper and Alden Bentley

NEW YORK/LONDON/TOKYO, March 27 (Reuters) - Global shares rose on Wednesday, nudged higher by a rally in Japanese stocks as the yen sagged to its weakest since 1990, while the dollar held mostly steady in a holiday-shortened week that ends with a key reading on U.S. inflation.

The yen, which has lost more than 7% in value against the dollar this year already, weakened to as far as 151.975 to the dollar, prompting Japan's three main monetary authorities to hold an emergency meeting on Wednesday to discuss the currency.

Market participants took this as a signal officials were ready to intervene in the market to stop what they described as disorderly and speculative moves in the yen.

"The news this morn was the Japanese yen. They're always concerned, even well before this for so many years, about hedge funds coming in and taking advantage of the yen," said Quincy Krosby, chief global strategist at LPL Financial, in Charlotte, NC. "So they typically come out with the warning to notify the market that 'we could come in and thwart your ambition in our currency market'."

The yen has been sliding despite the Bank of Japan's first interest rate hike for 17 years last week, as traders expect very gradual tightening and possible delays to long-expected Federal Reserve easing.

BOJ board member Naoki Tamura reinforced the dovish outlook on further tightening on Wednesday, saying the central bank should "move slowly but steadily toward policy normalisation".

Wall Street's main indexes rose at the open as chipmakers and growth stocks rebounded in light trading. The S&P 500 gained 29.63 points, or 0.57%, and the Nasdaq Composite gained 64.40 points, or 0.39%.

The Nikkei closed up 0.9%, although equities trading elsewhere was more subdued. MSCI's gauge of stocks across the globe rose 2.88 points, or 0.37%, to 781.41, while Europe's STOXX 600 index rose 0.12%.

"It's choppy, directionless trading, and there's a good reason for that: we've hit that time of the quarter when rebalancing flows are impacting the market," said Tony Sycamore, a strategist at IG.

Another reason is that two key events - the release of the U.S. Federal Reserve's favoured inflation indicator and public comments from Fed Chair Jerome Powell - come on Friday, when most markets are closed for a holiday, he added.

DOLLAR/YEN IN FOCUS

Against the Japanese yen, the dollar weakened 0.16% at 151.3. The dollar index was up 0.13% at 104.42, just below Friday's five-week high of 104.49, while the euro was down 0.15% at $1.0814.

"If there's any kind of intervention, it only has a significant lasting impact if the direction of travel has already begun to turn," Guy Miller, chief market strategist at Zurich Insurance Group, said.

"We've seen intervention in many countries over the years, but usually, while that can work in the very short term, you need to see the currency itself fundamentally change direction, and then policy intervention can reinforce that or exacerbate the move," he said.

U.S. 10-year Treasury yields were down slightly at 4.222%.

Traders are trying to gauge which of the big central banks - the Fed, ECB or Bank of England - will be first to cut rates this year.

Meanwhile, Sweden's Riksbank left interest rates unchanged but indicated it was likely to start easing monetary policy in either May or June.

Spot gold added 0.42% to $2,187.69 an ounce as it continued to search for a short-term floor following its surge to a record $2,222.39 last week. U.S. gold futures gained 0.43% to $2,186.60 an ounce.

Cryptocurrency bitcoin gained 2.17% at $71,330.00.

Oil fell for a second day after a report that crude stockpiles surged in the U.S., the world's biggest oil user, and on signs major producers are unlikely to change their output policy at a technical meeting next week.

Brent crude futures for May fell 0.35% to $85.95 a barrel. The May contract is set to expire on Thursday and the more actively traded June contract eased 0.61% to $85.11. U.S. crude lost 0.36% to $81.33 a barrel.

(Additional reporting by Dhara Ranasinghe in London and Kevin Buckland in Tokyo; Editing by Muralikumar Anantharaman, Kim Coghill, Jane Merriman, Andrea Ricci, William Maclean)