Stock trading app Robinhood is becoming a cryptocurrency broker.

Customers in California, Massachusetts, Missouri, Montana and New Hampshire will be able to trade bitcoin and ethereum through the app beginning in February, Robinhood announced Thursday. In the meantime, all customers can now track prices and receive alerts for 16 cryptocurrencies on the app.

The prices of bitcoin and other digital currencies surged last year as investors, including some on Wall Street, bet cryptocurrencies and the blockchain technology behind them could one day transform the world as much as the internet has. Bitcoin was developed as a way to send money around the world quickly and cheaply. However, transaction fees have soared above $20 and other digital currencies have yet to prove their actual use.

That hasn’t stopped investors from pouring in.

“Cryptocurrencies have become the first foray into investing and financial services to a large number of people,” Robinhood co-founder Vlad Tenev told CNBC in a phone interview. “Now it’s become more and more clear [that bitcoin is an] investing asset.”

That’s a change from October, when Tenev told CNBC that Robinhood was focused on expanding its stock trading business.

Still, “I wouldn’t call it a shift,” Tenev said. “We’re not seeing significant impact from cryptos on the size of the equity market. Marketwide, trading is increasing, investing is increasing.”

The company launched about three years ago as a way for customers, mostly younger investors, to trade stocks through their smartphones for free. Robinhood also has a premium paid service, and in December launched options trading. The company now has more than 3 million users, with 78 percent falling into the so-called millennial age category of 18 to 35 years old.

For cryptocurrency trading, Robinhood will have no investment minimums or maximums, and no withdrawal limits. The start-up will hold most of the digital coins offline in what is called cold storage. The practice prevents hackers from stealing the coins.

“We will connect to many exchanges, up to a dozen or more, over the next several months,” Tenev said. “We want to break even on this business, not to profit from it. We view this as an opportunity to expand our customer base and give our customers more access to functionality.”

List of digital coins Robinhood users can view

Source: Robinhood

But with just five states at launch Robinhood will not likely pose a significant threat to Coinbase, the leading U.S. cryptocurrency exchange. Coinbase has more than 13 million customers around the world and has money transmitter licenses in 36 states, including New York. The February rollout of cryptotrading to five states will be in phases, and Robinhood said it hopes to offer cryptocurrency trading to New York residents in the future, but noted that the state and others may require specific licensing and approvals.

Both fintech start-ups and more traditional players have been far more cautious about cryptocurrency trading. Some online brokerages such as E-Trade and TD Ameritrade offer access to bitcoin futures, but not the digital currency itself.

Online financial advisor Betterment said in a Jan. 16 blog post that cryptocurrency investing is like high-risk early stage investing in companies. The post also said that speculation is driving most of the price action in digital currencies today. Competing advisor WealthFront also said in December that it does not intend to incorporate bitcoin into its investment management service.

— CNBC’s Eugene Kim contributed to this report.