Amazon Web Services CEO Andy Jassy speaks at the 2017 AWS re:Invent conference in Las Vegas.

Amazon's cloud business generated more revenue than analysts expected in the fourth quarter, with sales surging 45 percent.

The financial results strengthen the case that Amazon Web Services has grown into a cash machine for its parent company, while Alibaba, Google, IBM, Microsoft and Oracle all try to catch up.

AWS captured $5.11 billion in revenue in the quarter and $17.46 billion in all of 2017, Amazon said in its quarterly earnings statement on Thursday. Analysts on average expected $4.97 billion, according to FactSet.

AWS now has a revenue run rate of over $20 billion, CFO Brian Olsavsky said during Amazon's conference call with analysts after the earnings release.

Operating income at AWS rose to $1.35 billion for the quarter, topping the FactSet estimate of $1.27 billion.