Bitcoin neared $50,000 for the first time on Tuesday, while the dollar declined and stock markets posted mixed results in reaction to an anticipated US fiscal stimulus and Covid vaccine developments.

Asia's main stock indices closed higher, with Tokyo hitting a 30-year high, while the Dow Jones index was off by 0.4 percent in early trading on Wall Street.

Bitcoin briefly pushed to a record-high of $48,215.82 after winning a huge boost Monday from news that Elon Musk's Tesla had invested $1.5 billion in the cryptocurrency.

It later eased back to a level above $46,000.

Stocks are benefitting from expectations of a strong economic rebound once vaccination programmes make more headway, but the optimism is being curtailed by delays to a potentially huge US stimulus plan. 

And President Joe Biden's $1.9 trillion rescue bill is now fuelling global inflation worries, alongside rising oil prices and the prospect of large consumer spending post lockdowns. 

"The real elephant in the room is what happens if oil prices continue to rise at their current rate," noted Michael Hewson, chief market analyst at CMC Markets UK.

Benchmark crude contract Brent North Sea held around 13-month highs above $60 on Tuesday thanks to surging demand expectations as economies reopen. 

"Oil's fundamentals are looking strong again on both (the) supply and demand side," said Edward Moya, analyst at Oanda trading group.

"Despite demand being down about five million barrels year-over-year, optimism is high that vaccine rollouts will have key parts of the global economy return to normal."

Axi strategist Stephen Innes said that market sentiment in general was buoyed also "by an upbeat set of earnings from the holiday season and vaccine optimism".

The inoculation drive "provides the ultimate recovery safety net that will allow people to participate on all those pre-Covid activities like the simple pleasures of going to a movie or having a meal out", he added.

In another sign of more upbeat times, crisis-hit Japanese carmaker Nissan upgraded its full-year forecast for the second straight quarter, as the global auto industry shows signs of recovery from the coronavirus pandemic.