April 30 (Reuters) - Three of the Wall Street's

heavyweight technology firms have reported better-than-expected

sales at their cloud computing units in recent days, as interest

in artificial intelligence drives a rebound in spending by

corporate customers.

Growth in the $270 billion cloud infrastructure market, a

cash engine for Amazon.com ( AMZN ), Microsoft ( MSFT ) and

Alphabet, gives the clearest sign yet that AI

investment is bearing fruit after investors drove those stocks

to record highs, thanks to optimism about the emerging

technology.

Many big customers have started spending again on cloud

computing after pausing last year to cut costs, executives and

analysts said.

Amazon ( AMZN ), the last of trio to report on Tuesday, said its

cloud computing arm AWS grew 17% in the January-to-March period,

above Wall Street's 15% growth estimate, and hit a $100 billion

annual run-rate for the first time.

Performance was consistent at Microsoft's ( MSFT ) Azure and Google

Cloud, which grew above expectations at 31% and 28%,

respectively, in the first three months of the year.

"Looking across AWS, Microsoft Azure and Google Cloud, it is

clear that two things are happening simultaneously - AI is

contributing to growth, but also the rest of cloud spending is

accelerating," said D.A. Davidson & Co analyst Gil Luria.

For several years cloud infrastructure providers enjoyed

growth rates as high as 60% and demand shot up during the

COVID-19 pandemic as more businesses moved online. However,

firms had to realign expectation last year as customer pulled

back spends in an increasingly challenging business environment.

The industry has been at the forefront of adopting AI and

customers had begun to buy the new functionality at a rapid

pace, executives said.

"The number of Azure AI customers continues to grow and

average spend continues to increase," Microsoft ( MSFT ) CEO Satya

Nadella said on the company earnings call, adding that more than

65% of the Fortune 500 companies were Azure OpenAI Service

customers.

AI services contributed 7 percentage-points in growth to

Azure, up from 6 percentage points in the Oct-Dec quarter.

More than 60% of funded generative AI startups and nearly

90% of genAI unicorns were using Google Cloud, Alphabet CEO

Sundar Pichai said on his company's earnings call last week.

"There is an inevitable and continuous migration of

workloads to the cloud and consolidation of IT spending going

towards large platforms, including the hyperscalers," said RBC

Capital Markets analyst Rishi Jaluria.

Hyperscalers are cloud providers with a large network of

data centers and wide range of services, and are often preferred

for end-to-end workload support.