(Reuters) - International Business Machines Corp IBM.N reported a bigger-than-expected decline in revenue for the first time in five quarters due to weak demand in its IT services business, a sign that the company's turnaround could take longer than expected.

A woman passes by the IBM offices in New York City, U.S., October 17, 2016. REUTERS/Brendan McDermid -

Shares of IBM, whose revenue has now fallen for 20 quarters in a row, tumbled 4.7 percent to $162 in trading after the bell on Tuesday. At current levels, the stock is set to more than erase its roughly 2.5 percent gain this year.

With demand for its legacy hardware and software businesses stagnating, IBM has been shifting towards cloud-based services, security software, data analytics and artificial intelligence such as its supercomputer Watson, which once defeated human contestants in the quiz show Jeopardy.

These “strategic imperatives”, spread across IBM’s various businesses, continued to grow in the first quarter, but failed to offset weakness in the company’s core operations, especially at the technology services and cloud platforms business.

IBM could not close some large deals in that business, which is its largest, while a couple of large clients took their operations in-house, Chief Financial Officer Martin Schroeter said on a conference call.

As a result, IBM’s overall revenue decline increased to 2.8 percent in the first quarter from 1.3 percent in the fourth quarter, and widely missed analysts’ expectation of a 1.6 percent drop.

“I think the frustration lies with the overall miss on revenue,” Edward Jones analyst Bill Kreher said.

“The Street has given IBM some credit over the last year that the transition is taking shape, so I think that’s where the risk lies ... execution needs to be strong.”

TURNAROUND TAKING TIME

IBM’s revenue of $18.16 billion in the first quarter missed analysts’ estimate of $18.39 billion, according to Thomson Reuters I/B/E/S.

Revenue in the technology services and cloud platforms business dropped 2.5 percent to $8.2 billion. The business accounted for about 45 percent of total revenue.

The company said gross profit margin fell in all five of its reporting units. Overall adjusted gross margin of 44.5 percent missed analysts’ estimates of 47.7 percent.

However, “strategic imperatives” revenue growth accelerated to 12 percent in the first quarter from 11 percent in the fourth.

Revenue from “strategic imperatives” was $7.8 billion in the latest quarter, accounting for 42 percent of total revenue, up from 37 percent a year earlier.

” ... The company at some point will see the newer businesses over take legacy, but it appears it’s going to take a little bit longer than previously believed,” Kreher said.

IBM’s net income dropped 13 percent to $1.75 billion. Excluding items, it earned $2.38 per share, beating analysts’ average estimate of $2.35.