The Mountain View, California-based Google did not say how much it had paid for Zagat Survey, which was founded in New York over 30 years ago and provides reviews of restaurants in more than 100 cities around the world.

"Zagat will be a cornerstone of our local offering -- delighting people with their impressive array of reviews, ratings and insights," said Marissa Mayer, Google vice president for local, maps and location services.

"With Zagat, we gain a world-class team that has more experience in consumer based-surveys, recommendations and reviews than anyone else in the industry," Mayer said in a blog post.

"Zagat provides people with a democratised, authentic and comprehensive view of where to eat, drink, stay, shop and play worldwide based on millions of reviews and ratings," Mayer said.

Purchasing the review guide would allow Google to apply the "power of Google search and Google Maps" to Zagat products, she said.

Zagat founders Nina and Tim Zagat said joining forces with Google is "the right next step for our employees, our users and for our business, all of which will benefit from the additional resources and reach that Google provides."

"Going forward, we will remain active in the business as co-chairs, helping to ensure that the combination of Zagat's and Google's assets and capabilities will maximise our product quality and growth," they said in a blog post.

"We are thrilled to see our baby placed in such good hands and to start today as official 'Googlers,'" they said.

Zagat, which relies on more than 350,000 contributors around the world but has only 100 full-time employees, has been facing competition online from free sites such as Yelp and has been for sale since January 2008.

Press reports at the time said Zagat was seeking USD 200 million.

Google's acquisition of Zagat comes nearly two years after it failed in a bid to buy Yelp.

OpenTable, another restaurant review site, saw its share price fall 8.13 per cent to USD 57.63 following the announcement that Google had purchased Zagat.

Google shares were up 0.47 per cent to USD 536.74 on Wall Street.