After a long period of quiet, the price of the virtual currency Bitcoin is surging again as signs of interest from China and Wall Street have helped kick off a new speculative frenzy.
The price of a single Bitcoin has been steadily rising in recent weeks. On Nov. 4, it spiked particularly sharply, rising above $500 on some exchanges, and bringing the value of a single coin up over 100 percent from a month ago. By the end of Nov. 4, the price had fallen back closer to $400.
The recent rally has been the biggest since the online currency entered a sustained decline after the collapse of what was once the biggest Bitcoin exchange, Mt. Gox, in early 2014. That incident — and the use of Bitcoin for drug sales — led many people to write off the virtual money as a passing fad.
Nonetheless, many banks and financial firms continued to study the technology behind the scenes and have recently been expressing their interest — and announcing new investments — in the technology underlying Bitcoin, which is being heralded as a new way to conduct a broad array of financial transactions.
There has also been a surge in demand for Bitcoin in China, where the new interest is being explained by a number of factors, including the drop in the stock market there, as well as the emergence of a new Ponzi scheme tied to Bitcoin. The price of Bitcoin has been rising faster on Chinese exchanges than elsewhere in the world.
Bobby Lee, the chief executive of one of China's biggest Bitcoin exchanges, BTCC, said that, as was the case in past price spikes, a critical mass of reports on Bitcoin was drawing a new wave of speculators, betting more on the future of the virtual currency than on its current use.
"There are a few tipping points in a row, and you get a tidal wave," Mr. Lee said. "It's classic bull market."