Bitcoin touched $15,000 for the first time on Thursday, extending its advance this month to more than 50 percent as concerns mounted the cryptocurrency’s rapid rise masks risks.

The world’s biggest cryptocurrency is surging on expectations that new bitcoin derivatives products expected to begin trading this month will boost mainstream demand. Some of the world’s biggest brokerages criticized those plans on Wednesday, telling regulators the contracts have been rushed to market without enough due diligence.

Bitcoin jumped as much as 18.4 percent to $15,797 on Friday, before paring gains to to $14,818 at 12:20 p.m. in London. That takes the digital currency’s surge this year to more than 1,400 percent and its market capitalization to $257 billion.

“This is irrational exuberance,” Royal Bank of Scotland Chairman Howard John Davies said in an interview on Bloomberg TV on Thursday. “This is a very, very unusual market, that shows we’re not in a normal two-way trading market.”

Davies agreed with the brokerages’ concerns that exchanges which are set to offer bitcoin futures and options have failed to get enough feedback from market participants on margin levels, trading limits, stress tests and clearing. Those warnings were laid out in an open letter via the Futures Industry Association on Wednesday.

Cboe Global Markets Inc. has said it will start trading bitcoin futures on Dec. 10, while CME Group Inc.’s contracts are set to debut on Dec. 18. Nasdaq Inc. is planning to offer futures in 2018, according to a person familiar with the matter. Cantor Fitzgerald LP’s Cantor Exchange is creating a bitcoin derivative, and startup LedgerX already offers options.

ASX Ltd., the main exchange operator for equities and derivatives in Australia, on Thursday said it will start using blockchain, the technology that underlies bitcoin, to process equity transactions. The digital currency also got a boost from a successful test of a technology that will attempt to ease congestion in purchases of the digital currency.

Lightning Network, the company behind the technology, is trying to move some transactions away from the blockchain by allowing buyers and sellers to transact privately and later broadcast their activity to the public network.

The price of bitcoin cash fell on the news, slumping 9.1 percent to $1,342.86, according to prices on coinmarketcap.com. The cryptocurrency rival offers a separate solution to bitcoin’s congestion issue.