Google and Microsoft have agreed to employ a raft of measures to block child sex abuse content by targeting more than 100,000 search terms.

The groundbreaking move by the leading search engine firms has been hailed by Prime Minister David Cameron, who will hold a cyber-summit later in the day.

Google's executive chairman, Eric Schmidt, says his company's 200-strong team has cleaned up the search teams which are generally used to locate child pornography material in cyberspace.

The measures will soon be applied to more than 150 languages across several countries.

Schmidt, in an article in the Daily Mail, wrote: "We've listened. We've fine-tuned Google Search to prevent links to child sexual abuse material from appearing in our results.

"We're now showing warnings - from both Google and charities - at the top of our search results for more than 13,000 queries. These alerts make clear that child sexual abuse is illegal and offer advice on where to get help."

New algorithms have been introduced in the search engines of Google and Microsoft to throw up cleaner results.

Google and Microsoft's Bing together account for nearly 95% of search traffic in cyberspace.

The announcement of the new measures came a day before the Downing Street summit where Cameron, along with US law enforcement agencies, is expected to introduce a series of reforms to tackle online child sexual abuse material.

The Internet Safety Summit will also be attended by Google and Microsoft.

Cameron told the Mail: "Google and Microsoft have come a long way. A recent deterrence campaign from Google led to a 20% drop off in people trying to find illegal content, so we know this sort of action will make a difference."

He warned that the government will bring forward legislation if the firms did not keep up their promises.

Cameron is also set to reveal a transatlantic task force formed by Britain's National Crime Agency and America's FBI to effectively combat criminals and paedophiles who operate secretly on the internet.

The authorities will also discuss ways to target the offenders who use encrypted networks and other secret methods to distribute illegal material.