Advertisers are starting to shift search spending from Alphabet's Google to Amazon, in a sign that the home appliance giant is using its preferred channel for consumer search to encroach on Google's online advertising moth.

WPP, the world's largest advertising buyer, spent about $300 million on Amazon search ads on behalf of customers last year, about 75 percent of which came from budgets that were due to be spent on platforms, people familiar with the matter said. In 2017, the company spent between $100 million and $150 million on Amazon searches, according to people familiar with the matter.

WPP committed more than $3 billion globally to Google's search ads last year, according to one person familiar with the matter.

Omnicom Group, another big ad buyer, said 20 to 30 per cent of its customers' spending on search ads last year went to Amazon's search ads, most of which were also funded by Google's original search budget. The New York advertising agency spent about $1.2 billion on search ads in the U.S. last year, according to people familiar with the matter.

But Amazon has a long way to go to catch up with Google. Google accounts for 78 percent of the $44.2 billion U.S. search advertising market in 2018, according to eMarketer, a research firm.

But according to data collected by Jumpshot, a research firm, from 100m devices, a major shift is taking place on the consumer side: while Google has long monopolized the internet search market, 54 per cent of consumers search for an item directly on Amazon, up from 46 per cent in 2015.

"Consumers no longer hesitate between Google and Amazon, and most of them go straight to Amazon," said Scott Hagedorn, Acer's chief executive.

Mr. Hagdorn said the shift to Amazon's ad-search revenue comes from companies that sell products on its platform, such as consumer-goods packaging manufacturers and retailers.

Google and Amazon declined to comment.

The eMarketer company didn't give an exact figure for Amazon's search ad revenue or how much it added, but estimated it would account for at least half of Amazon's $11.3 billion in ad revenue this year.

That means Amazon will be second only to Google in this area, and Microsoft is expected to account for 6.7 percent of the U.S. search advertising market this year.

Google's spending on search advertising continues to grow and is expected to grow 17 per cent this year to $40bn, according to eMarketer. However, Google's market share is expected to fall to 71% by 2020 as Amazon grows, the research firm said.

Executives at the advertising agency say Amazon's advantage is its ability to tell advertisers whether their ads translate directly into product sales.

"The transition from Google to Amazon Search is really simple, " says Shane Atchison, chief executive of WPP's North American business, Wunderman Thompson.

Amazon's advertising ambitions are growing steadily. In addition to search, it offers marketers other opportunities, including display ads, TV ads on live sports, and targeted ads that people run online. Overall, it is now the third-largest digital advertising ad ad ad company after Google and Facebook.

Search ads on Amazon's website are called "sponsored ads" and when users enter search terms such as "shampoo," the company bids in an auction-based system to have their products appear in turn.

Oars and Alps, the maker of men's beauty products, used Google search ads last year, but the company has shifted most of its search spending to Amazon. Its monthly advertising spending with Amazon now exceeds $20,000.

"I was surprised by the return on Amazon's advertising spending, so I reduced our spending on Google searches," says Laura Cox, co-founder of Oars and Alps. "

Advertising executives say the increase in Amazon's search spending also comes from other advertising and marketing budgets, including in-store promotions and display ads. Dentsu Aegis Network, another major advertising buyer, said amazon's search spending in the U.S. rose more than 60 percent last year, but only a small portion of that could come from the budget previously earmarked for Google.

Amazon does not sell search ads to companies that don't sell products on its website, such as financial services, insurance and car companies, and they will continue to drive Google's advertising business.

Amazon is also testing video search ads, a move that could help attract more search money. "The challenge is more to bring in more brand-driven advertisers, and video may help make that happen," said Vin Paolozzi, executive vice president of innovation at Magnam Global, Interpublic's advertising buying arm. "

Advertising executives also say there are drawbacks to the influx of advertising money to Amazon: advertising prices for competing products such as consumer goods have risen sharply. Last month, for example, the cost per click of a "laundry detergent" search term was $17.51, up 127 percent from September, according to data from Pacvue. Pacvue is a brand-optimized platform for Amazon's ads.