Asian shares struggled on Tuesday after a healthcare mega-merger failed to impress Wall Street, while the dollar took a breather from its run to 8-month highs on rising convictions that the Federal Reserve will raise interest rates next month.

MSCI's broadest index of Asia-Pacific shares outside Japan wavered in and out of positive territory, and was last down 0.2 per cent.

Japan's Nikkei dipped about 0.1 per cent after a long weekend. Markets were closed for a national holiday on Monday.

"We're post Japan Inc earnings now and the focus is back on China where local brokers are talking about market reforms, many of which have direct market impacts, which is important because China is a policy-driven market," said Gavin Parry, managing director of Parry International Trading.

"There's also a continued focus on the US Federal Reserve, with a lot of sell-side banter about quantifying what level of rate increase brokers are expecting," he said.

Chinese shares dropped, with the blue chip CSI300 index of the largest listed companies in Shanghai and Shenzhen down 1.2 per cent and the Shanghai Composite Index down 1 per cent.

On Monday, Wall Street edged down as Pfizer's plan to buy Allergan Plc in a $160 billion deal quickly drew criticism from politicians as a tax dodge.

"Investors may feel that even if this deal comes through, this will become the last of this sort," said Yoshinori Shigemi, global market strategist at JPMorgan Asset.

Markets showed no immediate reaction to a worldwide travel alert issued by the US State Department, that warned US citizens of the risks of travelling because of what it described as "increased terrorist threats."

The dollar index, which tracks the US unit against six major rival currencies, edged down about 0.1 per cent to 99.683, after it rose to an 8-month high of 100.00 overnight, within sight of its 12-year peak of 100.39 touched on March 13.

Whether the dollar can rise above that peak could depend on the pace of the Fed's rate hikes next year. Markets are currently pricing in two more rate hikes next year after a likely December move.

In contrast to the Fed, the European Central Bank is widely expected to add stimulus next week, including deepening its already negative interest rates that make banks pay, not receive, interest on their deposits at the central bank.

The euro edged up slightly to $1.0637, after falling to a 7-month low of $1.0592 in US trade on Monday.

Precious metals were under pressure. Spot gold edged up about 0.1 per cent to $1,070.40 an ounce but remained not far above last week's near six-year low. Silver also touched six-year lows overnight, while platinum dipped to a fresh seven-year low on Tuesday.

Base metals were also pressured, suffering from concerns about slowing demand from China.

Copper, which has fallen more than 12 per cent so far this month, stood at $4,463 per tonne, down about 0.6 per cent and not far from a 6-1/2-year low of $4,443.50 hit on Monday.

But crude prices won a reprieve after Saudi Arabia pledged to work toward oil price stability.

US crude futures were off earlier highs but still up 0.5 per cent at $41.95 per barrel, up from a three-month low of $38.99 hit on Friday. Brent added 0.5 per cent to $45.03. – Reuters