SAN FRANCISCO - Google on Wednesday started to try a new search feature which would enable its web search engine results to integrate information from users' personal email accounts such as Gmail.

"Sometimes the best answer to your question isn't available on the public web -- it may be contained somewhere else, such as in your email," Amit Singhal, Google's senior vice president in charge of search, wrote in a post on the company's blog.

"Starting today, we're opening up a limited trial where you can sign up to get information from your Gmail right from the search box," he said.

Singhal noted that the new feature is an attempt to make Google 's search results to be "truly universal."

As an example cited by Google, when singed up users search for "my flights" on Google's public web search engine, they will see their flight confirmation emails for any upcoming trips right on top of the search results.

Google said the field trial of the new feature is now only accessible on its search website google.com in English.

Singhal also announced that an enhancement to its search service, called Knowledge Graph, will now be extended to users in every English-speaking country after its launch in the United States in May 2012.

With the Knowledge Graph, users will see a panel on the right- hand side of the Google search results page, which provides a summary of key facts about users' search with the most useful and interesting information related to the particular topic.

According to Google, the Knowledge Graph feature is based on its database which now includes more than 500 million real-world people, places and things with 3.5 billion facts about and connections among them.

In another update to its search engine, Google on Wednesday said that it will soon offer voice search in its search applications for users of Apple's iPhone and iPad following the availability of the function on devices running Google's Android operating system.