Asian traders shifted cautiously on Tuesday with Chinese stocks swinging back and forth, while concerns grew about the future of the much-vaunted US tax reforms.

After months of gains across global equities, investors are taking a step back on unease that some valuations may be too high, though bitcoin continued its surge to new records and was on course to break the $10,000 mark.

Shanghai ended a volatile day up 0.3 percent, having lost more than three percent since Wednesday with mainland dealers spooked by Beijing's crackdown on risky dealing.

A warning from authorities last week about the sharp rise in one of the country's best-performing stocks added to worries. Analysts have also noted a lack of intervention by state-backed firms to support key issues, indicating a willingness to see prices fall to cool the market.

Greg McKenna, chief market strategist at AxiTrader, also pointed out that several data reports have undershot expectations recently, raising worries about the Chinese economy.

"That means the first two weeks of December, when we get the next monthly update on the Chinese economy, are going to be very important," he added.

Hong Kong pared early losses to end marginally lower. Tokyo was slightly down while Sydney closed down 0.1 percent. Singapore was flat and Manila shed more than one percent.

 

- Bitcoin targets $10,000 -

 

Seoul ended 0.3 percent up, reversing an early sell-off on reports of activity at a North Korean missile base, raising fears it may be preparing another missile test.

The news also sent the yen rallying against the dollar initially on a chase for safety, though it gave back the gains later in the day.

In early European trade London and Frankfurt each rose 0.1 percent, while Paris added 0.2 percent.

Eyes are now on Washington where senators are expected to vote on Donald Trump's tax-cut plans, but there are fears his Republican party might not be able to muster enough votes to push it through.

While the passage of the bill would likely fire up global markets, analysts are concerned its failure could lead to a correction.

Expectations Trump would push through his market-friendly measures of cutting taxes, ramping up infrastructure spending and cutting red tape have helped fuel a global rally.

However, Republican infighting -- at least two senators are presently ready to vote it down -- has led to concerns that the tax reform could collapse in similar fashion to the overhaul of healthcare.

This week sees a series of other potentially market-moving events, with the congressional hearing for Jerome Powell, Trump's pick as the next Fed boss. Current governor Janet Yellen is also due to speak and official US growth figures are to be released. 

Bitcoin hit a new peak of $9,895.68 as it homed in on $10,000, fuelling worries of a bubble.

The world's biggest cryptocurrency has ballooned since it hit a 2017 low of $750 in January, and it has seen a jump of more than 16 percent since Friday alone.

Analysts said the unit's stratospheric rise has attracted huge interest from speculators looking for a quick return with global stock prices considered too high.

"The weekend's bitcoin price hike is just the continuation of a long-term bull run on the cryptocurrency, fuelled by the tsunami of speculative trading on Japanese exchanges and the entrance of institutional investors across the world," Thomas Glucksmann, Hong Kong-based head of marketing at cryptocurrency exchange Gatecoin, told Bloomberg News.

"It is more likely that the $10,000 psychological stratosphere will push more institutional investors into the mix."

 

- Key figures around 0820 GMT -  

 

Tokyo - Nikkei 225: FLAT at 22,486.24 (close)

Hong Kong - Hang Seng: FLAT at 29,680.85 (close)

Shanghai - Composite: UP 0.3 percent at 3,333.66 (close)

London - FTSE 100: UP 0.1 percent at 7,387.68

Euro/dollar: UP at $1.1900 from $1.1899 at 2140 GMT

Pound/dollar: UP at $1.3325 from $1.3321

Dollar/yen: UP at 111.27 yen from 111.09 yen

Oil - West Texas Intermediate: DOWN 33 cents at $57.78 per barrel

Oil - Brent North Sea: DOWN 18 cents at $63.66 per barrel

New York - DOW: UP 0.1 percent at 23,580.78 (close)