(Reuters) - Microsoft ( MSFT ) missed Wall Street estimates for quarterly growth in its Azure cloud-computing service on Tuesday, another sign it may take longer for Big Tech to benefit from hefty spending on AI technology.

Shares of the Redmond, Washington-based firm fell 7% in extended trading and sparked a sell-off in major tech stocks with Amazon.com and Nvidia down 4.5% and 10%.

Microsoft's ( MSFT ) shares have climbed nearly a quarter in the past 12 months on optimism that the company is the frontrunner in the AI race thanks to its investments in ChatGPT maker OpenAI.

But some of that investor enthusiasm has given way in recent weeks to worries that runaway spending by tech giants on AI infrastructure would yield little payoff in the short term, pushing down shares of Microsoft ( MSFT ) nearly 6% this month.

Microsoft ( MSFT ) said revenue from its Intelligent Cloud unit - home to the Azure cloud-computing platform - rose to $28.5 billion in the quarter ended June 30, missing analysts' estimates of $28.68 billion, LSEG data showed.

Azure revenue rose 29%, lower than the 30.6% growth estimate from market research firm Visible Alpha. Microsoft ( MSFT ) does not break out the absolute revenue figure for Azure, the part of its business best situated to capitalize on booming interest in AI.

The miss came as the Windows maker is pouring billions of dollars into data centers to prepare for a potential surge in demand for AI services.

The company's capital expenditure including finance leases rose 77.6% in the quarter to $19 billion. It also marked a big step up from the $14 billion it recorded in the previous three months.

Microsoft ( MSFT ) has said the spending was needed to expand its global network of data centers and overcome the capacity constraints that were hampering its efforts to meet AI demand.

CEO Satya Nadella has pushed the company to go all-in on the technology, weaving AI into almost every product from search engine Bing to productivity software such as Word.

Large parts of those efforts have been fueled by technology from OpenAI, in which Microsoft ( MSFT ) has invested about $13 billion, including the 365 Copilot assistant for enterprises that costs $30 a month and became widely available last year.

Microsoft ( MSFT ) - seen as a bellwether for the tech industry thanks to its wide-spanning business - said total revenue rose 15% to $64.7 billion in the quarter to June, its fiscal fourth quarter. Analysts had expected $64.39 billion, according to LSEG data.

(Reporting by Aditya Soni and Yuvraj Malik in Bengaluru; Editing by Sriraj Kalluvila)