Bitcoin surged past $18,000 after it began trading on its first major global exchange Sunday, the latest in a series of highs that have excited some investors while leaving others nervous of a bubble.

Trading of the controversial digital currency on a futures contract began at 6:00 pm (2300 GMT) on the Chicago board options exchange (Cboe) at a price of $15,000.

Heavy traffic made the Cboe website inaccessible in the first 20 minutes, but it said that "trading runs on very separate systems and was totally unaffected by the website issues." 

Around 0320 GMT, bitcoin was trading at $17,750 per unit for the futures contract expiring on January 17, thus exceeding the highest value it had reached on alternative non-regulated internet platforms. It even climbed past $18,000.