Businesses are set to spend more on mobile internet advertising than for ads seen via desktop computers for the first time in 2017, forecaster ZenithOptimedia said on Monday, a year earlier than it had previously predicted.

Zenith said it expected companies around the world to spend $99.3 billion on mobile internet advertising in 2017, or 2 percent more than the amount it expects to be spent on ads seen on web pages on desktop computers.

"We now expect desktop advertising to decline for the rest of our forecast period: by 0.9 percent in 2016, 0.4 percent in 2017 and 6 percent in 2018," ZenithOptimedia said.

ZenithOptimedia, owned by France's Publicis, cut back its expectation for growth in global advertising this year for the second time to 4.1 percent from a previous forecast of 4.6 percent in March.

Mobile phone user
A man uses his mobile phone in central London Aug. 30, 2013. REUTERS/Olivia Harris

In its report on Monday, Zenith cited the devaluation of the Argentine peso for the forecast revision.

It also said the top six global advertising markets would remain stable between 2015 and 2018, during which time it expected China to be the biggest contributor to new advertising spending, ahead of the United States.