Google CEO Sundar Pichai said the company's cloud unit reached $8 billion in annualized revenue and plans to triple its sales force over the next few years.

Google's cloud is a key growth driver for Alphabet, Pichai said on Thursday's second-quarter earnings call.

The hiring efforts come as Google Cloud chief Thomas Kurian, who has led the business for seven months, chases down Amazon and Microsoft. Kurian promised earlier this year to aggressively increase its sales team.

Amazon Web Services, the leader in cloud infrastructure, reported 37% growth on Thursday to $8.38 billion, which makes it about quadruple the size of Google's business.

Microsoft, the No. 2 player, said last week that Azure grew 64%. Jay Vleeschhouwer of Griffin Securities estimated in a note last week that Microsoft picked up $4.1 billion in Azure revenue in its second quarter. That suggests Azure is about double the size of Google's cloud.

Alphabet said Tuesday that its "other" revenue, which includes cloud, came in at $6.18 billion compared to $4.43 billion in the prior year. Kurian, who has been charged with growing the business, has already made a few acquisitions, including analytics company Looker.

Cloud boosted Alphabet's overall second quarter earnings, according to Alphabet finance chief Ruth Porat. Shares of Alphabet rose more than 9% Thursday after the company reported $38.94 billion in revenue, topping the $38.15 billion expected.

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