San Francisco-based data-storage company Dropbox Inc. opened up around 40 percent Friday relative to its initial public offering price, with investors showing enthusiasm for the United States' biggest tech IPO in more than a year.

Hours before its 11.35 am debut on the Nasdaq, the company had announced an IPO price of $21 a share.

But the stock, which is trading under the ticker symbol DBX, opened at $29 and then continued to climb, rising to around $31 a share 15 minutes into its trading session.

It had fallen back though shortly after 2 pm to $29.33 a share, a gain of around 39.7 percent from the IPO price.

Dropbox's debut is the biggest tech IPO since Snap Inc., the owner of multimedia messaging app Snapchat, went public on March 2, 2017.

The cloud-storage specialist, which made an initial public offering of 36 million Class A shares, was looking to raise $756 million through the IPO.

Founded in 2007, Dropbox has more than 500 million registered users - most of which use its free service that offers limited storage capacity - and a presence in 180 countries.

Around 11 million users pay for a more advanced service.

Dropbox, which faces strong competition from tech giants Apple and Google, posted slightly more than $1.1 billion in revenue and a net loss of nearly $112 million last year.

The company's main shareholders are venture-capital firm Sequoia Capital and its co-founder and CEO, Drew Houston.