Asian shares held tight ranges on Tuesday before the a Federal Reserve policy meeting, but were broadly supported close to six-months on anticipations the central bank may strike a dovish tone, while fresh Brexit worries persistent the pound.

MSCI’s widest index of Asia-Pacific shares outside Japan was flat, easing back from its highest level since September 21 hit previous in the session.

Japan’s Nikkei average plunged 0.3 percent, while Australian stocks eased 0.1 percent.

Chinese stocks held tight ranges, with benchmark Shanghai Composite floating almost flat, the blue-chip CSI 300 falling 0.2 percent, and the Hang Seng border 0.1 percent lower.

All three major U.S. indexes increased all-night, raised by the bank and technology sectors, with the Dow Jones Industrial Average, the S&P 500, and the NASDAQ Composite adding between 0.3 and 0.4 percent each.

"Speculators appear to be betting on a rise in stock prices on the back of a dovish Fed. The Fed is unlikely to kill such hopes. Yet there is a risk the Fed could tone down its dovishness," said Masanari Takada, cross-asset strategist at Nomura Securities.

With worldwide financial development appearing to sluggish, traders were focused on the Fed gathering, which kicks off its two-day policy meeting later in the day, for clues about the likely path of U.S. borrowing costs.