Bitcoin prices fell from a high of $1,240 to a low of $870 this morning. This is according to data from Bitcoin exchange Mt. Gox.

That $370 drop can by characterized as a 30% crash.

Earlier today, the People's Bank of China warned that the controversial electronic currency carried risk. It also instructed financial institutions not to trade it.

"Is this a bubble in Bitcoin?" asked former Federal Reserve Chairman Alan Greenspan Wednesday on Bloomberg. "Yeah it's a bubble."

"This is worse than the tulip mania," said Nout Wellink, former president of the Dutch Central Bank. "At least then you got a tulip [at the end], now you get nothing."

Bitcoin has bounced back a bit and it's currently straddling the $1,000 level, which means it's down by around 20% from its high.

Here's a look at the chart from Clark Moody.