Facebook has offered reassurances to investors that its digital ad business would remain highly profitable, despite a dip in usage on the social media network and an overhaul of its flagship News Feed. 

The company said in an earnings report that quarterly revenue jumped 47% from a year earlier.

Executives said on a conference call that they saw more chances to make money even if people spend less time on Facebook. 

Analysts had wondered about the resilience of the world's largest social media network, which is making changes to its products to deter foreign influence campaigns such as the ones that it says Russia has carried out and to stem the spread of sensationalism. 

Facebook added to jitters last night when, in its earnings report, it said that at the end of last year time spent by users had fallen by about 50 million hours a day. 

Its shares fell more than 4% in after-hours trading on Wall Street. 

But Facebook executives expressed optimism on calls with analysts.

They said the changes they were making in response to criticism would be healthy for the business in the long term and might not even hurt much in the short term. 

"I want to be clear: The most important driver of our business has never been time spent by itself. It's the quality of the conversations and connections," chief executive Mark Zuckerberg said.

The upbeat forecast led to a rebound in shares, which in late after-hours trading were up 1.4% at $189.50. 

Facebook's chief operating officer Sheryl Sandberg told analysts that recent changes to reduce disinformation on Facebook could create "more monetisation opportunities".

Ms Sandberg said she was optimistic about potential revenue from ads on "stories" on Facebook and Instagram, while chief financial officer David Wehner said the average price per ad increased 43% in the quarter.

Facebook said that time spent was falling at the end of last year by about 50 million hours a day due to changes that it said reduced viral videos, even before the company announced a series of changes to the News Feed that may further reduce user engagement. 

Facebook's 1.4 billion daily active users was up 14% from a year earlier, but below analysts' estimate of 1.41 billion for the fourth quarter, according to financial data and analytics firm FactSet. 

The number of daily users in the US and Canada fell for the first time in Facebook's history, dipping in the company's home market by 700,000 from a quarter earlier to 184 million. 

Total revenue, though, showed little impact, rising 47% to $12.97 billion and beating analysts' estimate of $12.55 billion, according to Thomson Reuters.

Wehner reiterated Facebook's earlier guidance on expenses, telling analysts on the call that expenses would likely grow 45-60% during 2018. 

The spending spree includes thousands of new workers to review content posted by users. 

The overhaul of Facebook's New Feed was prompted in part by its disclosure last year that Russian agents used Facebook to try to sway American voters from 2015 to 2017, an allegation that Moscow denies. 

Facebook said 126 million Americans may have seen Russian-backed political ads and posts. 

The company said that net income attributable to Facebook shareholders rose to $4.27 billion, or $1.44 per share, in the fourth quarter ended December 31 from $3.56 billion, or $1.21 per share, a year earlier. 

Excluding a tax provision, the company earned $2.21 per share, topping analysts' estimates of $1.95, according to Thomson Reuters. 

Facebook said it increased its provision for 2017 income taxes by $2.27 billion, citing US tax changes.